Petroleum Exploration and Development

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Successive generation of natural gas from organic materials and its significance in future exploration

ZHAO Wenzhi; WANG Zhaoyun; ZHANG Shuichang; WANG Hongjun; ZHAO Changyi and HU Guoyi

, 2005, 32(2): 1067-0.

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The mechanism of natural gas successive generation from organic materials means that the organic material converts with development of geothermal evolution from the kerogen thermal degradation to the thermal cracking of liquid hydrocarbon or soluble organics specifically in coal measures, leading to the relay contribution of natural gas generation from kerogen degradation to liquid hydrocarbon cracking at different stages of thermal evolution. The successive generation model of natural gas contains two aspects of ideas: ①The gas generated from kerogen thermal degradation generally takes place earlier than those from liquid hydrocarbon or soluble organic cracking. The gas generative dynamics of different organic matter shows that the major gas generation period from Ⅰ,Ⅱ and Ⅲ types of kerogen occur respectively in the thermal evolution stages of Ro＜1.6% (Ⅰ,Ⅱ) and Ro<1.3%. The major thermal cracking gives from liquid hydrocarbon or soluble organics are mainly occurred in the thermal evolution stages at Ro＞1.6% and Ro＞1.3%, respectively; ②Liquid hydrocarbon generated from kerogen degradation can only expel partially from source rocks and accumulated in appropriate place of reservoirs. A big portion of the liquid hydrocarbon still remains scattered in source rocks, which will be thermally cracked into gas with the increase of geothermal evolution, especially in high to super-maturation stages with the Ro＞2.0%.The model will help to understand the mechanism of natural gas accumulation with the feature of late gas generation from highly matured source rocks, and it is of great importance with the setup of this model to reveal the valuable potential of further exploration in the regions and intervals with high to super-high maturation.

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Oil-source correlations for high and over matured marine source rocks in South China

LIANG Digang and CHEN Jianping

, 2005, 32(2): 1068-0.

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The high and over matured marine source rocks, with vitrinite reflectance value (Ro) over 1.3% and 2%, respectively, widely developed in South China, in which abundant paleo-oil traps and oil showing have been found. Some common biomarkers as isoprenes, sterane and terpane have been used for correlating of oil and source. With the increase of maturity, it might be a big problem since the biomarkers extracted from oils, bitumen and source rocks would become a similar developing pattern, lose their original significations and are hardly to be used for the correlations. The carbon isotopic composition shows a clear fractionation of thermal evolution and it is difficult for precious correlating. The researches on the samples from Shiwandashan Basin suggest that triaromatic steroid could be practically used for identifying different strata and lithological rocks, including mudstone and limestone source rocks, under high and over matured conditions, so triaromatic steroid is very likely to be an effective tool for correlating in these cases. Correlations show that the effective source rocks in South China are mainly mudstone but not carbonate. This correlation method and biomarkers could be widely used for oil-source correlation of high and over matured source rocks developed in either north or south China.

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Chinese natural gas resources

LI Jingming; LI Jian; XIE Zengye; LIU Renhe and WANG Hongyan

, 2005, 32(2): 1069-0.

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China is rich in natural gas resources and the prospective reserves and producible reserves are up to 47×1012m3 and 14×1012m3, respectively. The gas resources distribute mainly in 11 basins as Ordos, Tarim, Sichuan, Qaidam, East China Sea, Ying-Qiong, Songliao, Zhujiangkou, Bohai Bay, and Junggar Basin, etc. The resources in west, east China and sea area are about 80%, 8% and 12%, respectively. The gas resources could be divided into 5 types based on their reservoir types: conventional gas, low permeability gas, extremely low permeability gas, carbonate fracture gas and carbonate porosity gas. The gas exploring realms are mainly in Sichuan, Ordos, Tarim, Qaidam and deep layer of Songliao Basin on land and in Eastern China Sea, Ying-Qiong and Zhujiangkou Basin on Ocean. China is also rich in coal bed methane resources. Its prospective reserves are 27.3×1012m3.

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Inhomogeneity of oil and gas distribution and its controlling factors in Kuche Depression, Tarim Basin

QIN Shengfei; PAN Wenqing; HAN Jianfa; SONG Yan and HONG Feng

, 2005, 32(2): 1070-0.

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The distribution and geochemistry characteristics of oil and gas in Kuche Depression, Tarim Basin, is inhomogeneous, which may have been controlled by: ① different levels of maturity of source rocks, ②different geochemical characteristics of the gases, and ③different source rocks. In the areas with poor cap rocks or destructive fractures, the gas has largely dissipated and the remaining oil formed relic oil reservoirs. Kuche Depression has experienced multiple phases of reservoir formation and structural movement, trapping different-stage generations of oil and gas.

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Definition and abundance threshold of marine source rocks developed in South China

CHEN Anding

, 2005, 32(2): 1071-0.

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Because the marine strata in South China has complex tectonic setting and the hydrocarbon generating process for some old source rocks, as Cambrian shale, is too early, an additional definition on marine effective source rock suggested that the source rock must have contributed to the present traps or the late reservoir formation. It is proposed that the time limitation and associated index should be added to the evaluation of old source rocks. The sedimentary environment controlled the development of carbonate source rock and the algae carbonate is uppermost source rocks in carbonates. For effective source rocks with variable maturity,the threshold of organic carbon content should be different.

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Three delta deposition systems and reservoir property correlation in Subei Basin

ZHONG Siying; SHAO Xianjie; LIAO Guangming; CHEN Zhixiang and WANG Pei

, 2005, 32(2): 1072-0.

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Subei Basin is composed of a series of small rift basins. Different delta systems such as fan delta with coarser, low rounded and badly sorted gains are developed on precipitous slop, closing to source rock. Channel sand bodies in fan delta plain with low physical properties are not effective oil and gas reservoirs. Its submerged branch channel and sand sheet are the important reservoirs. Braided delta usually developed on middle part of the slop. Braided rivers are well developed on fan delta plain. Gravity flow channel and turbidity currents are often found on fan delta-front zones. The distributary mouth bar, distal bar, sand sheet and submerged branch channel could be the important play targets. Normal delta with thin and well sorted grains developed on low slop and accompanies shallow lake facies. Biotic clastic limestone, beach bar and distributary mouth bar with thick sand could be the beneficial reservoirs.

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Features of gas accumulation and exploration foreground in oolitic reservoir of Feixianguan Formation in Sichuan Basin

XIE Zengye; TIAN Shicheng; SHAN Xiuqin; YANG Wei and LI Jian

, 2005, 32(2): 1073-0.

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The biggest oolitic gas field has been found at Feixianguan Formation in northeast Sichuan Basin,which belongs to the dynamic system of other source, high press and vertical migration. The natural gas is the dry gas with high content of H2S, and mainly comes from the cracking of foregone pool. The high content of H2S in gas component is contributed to the thermochemical sulfate reduction. The gas accumulation is controlled by palaeohigh. The natural gas distributes under the territorial caprock of gypsum and salinastone at Leikoupo Formation of Middle Triassic, and accumulates in the encirclement controlled by fault. Of all pool forming conditions, encirclement and oolitic reservoir are the two major factors. The provision capability of oolitic reservoir has been greatly improved by dolomitization and corrosion of organic acid and sulfur acid. These oolitic gas reservoirs contain two kinds of forming models, namely, lithology-structure and structure. It belongs to the type of late hydrocarbon accumulation for pool forming that undergo the process of the petroleum accumulation at late Indo-Chinese epoch-Yanshan movement, and adjustment at Himalayan movement. The oolitic reservoir has a good exploration foreground due to the wide distribution and the huge resource potenial.

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Control factors for forming higher porosity and permeability sandstone reservoirs in Chang 8 member of Yanchang Formation, Ordos Basin

WANG Xinmin; GUO Yanru; FU Jinhua; LIU Huaqing; CHEN Qilin; LI Tianshun; LIAO Jianbo and ZHANG Chunlei

, 2005, 32(2): 1074-0.

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The Chang 8 member sandstone reservoir, Triassic Yanchang Formation , Ordos Basin, developed in NE deltaic sedimentary system and SE braided stream delta sedimentary system, which are mainly debris-feldspar and feldspar-debris sandstone with low porosity and penetrability. The geological data suggest that the key factors for the primary pore conservation are sedimentary facies (sand sheets, distributary channel and mouth bar), abnormal pressure difference, early hydrocarbon filling, chlorite lining and cementation of dispersive quartz. Organic acidization developed the secondary pores, which in turn improved the physical property. These areas are potential high porosity and permeability reservoirs.

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Formation mechanism of Paleogene low permeability reservoir in Dina 2 gas field, Tarim Basin

YANG Fan; SUN Yushan; TAN Xiucheng; ZHANG Lijuan and WANG Yuehua

, 2005, 32(2): 1075-0.

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The main reservoir of Dina 2 gas field in Kuche Depression, Tarim Basin, is clastic rock with low permeability and porosity. The oil and gas are mainly produced from siltstone and muddy siltstone. The coarse clastic rock of the braided channel of the fan-delta plain is formed when sedimentary water body is in the salinity stage of active tectonic period, the cotemporaneous cementation is intense and the cementation of the carbonate and sulphate has intense packing action in eogenetic stage of shallow buried. The siltstone and muddy siltstone of the fan-delta front is formed from further source area and lower salinity of the water body in the relatively quiet tectonic period, with relative high compositional maturity and textural maturity, weak cotemporaneous cementation, more primary pore, weak cementation in the eogenetic stage and intense solution of the late diagenetic.

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Lower Carboniferous sediment sequence and sandbody forecasting in Hade area, Tarim Basin

SHEN Yinmin; SUN Yushan; GU Qiaoyuan and XU Xun

, 2005, 32(2): 1076-0.

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Rich information from cores and well logs, principles and tools of sedimentology and high-resolution sequence stratigraphy, were used for a delicate sequence analysis of the thin marine reservoirs in lower-mudstone section, Lower Carboniferous in Hade area, Tarim Basin, which are low energy sandy coastal sediments of highstand system tract of sequenceⅠ, consisting of many shallow-up coarse para-sequences which builds an aggression parasequence set. With the slow fall of sea level, the environment of HST was gradually changed to the alternative environments of offshore and shoreface-foreshore, and finally changed to coastal plain. Five thin-sand-beds are separated by marine mudstone into isolated sheet lenticles, and changed to mudstone laterally. The sand direction is nearly NW to SE, distributed along palaeo-shoreline. These beds are obviously controlled by sequence setting, palaeo-geomorphology and sediment supply. Some huge stratigraphic reservoirs mainly controlled by lithology could be the potential petroleum play targets.

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Trapping conditions of shallow gas accumulation in Subei Basin

ZHANG Dongling; BAO Zhidong and LIU Ping-lan

, 2005, 32(2): 1077-0.

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Trapping conditions of shallow gas accumulation in Subei Basin

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Source and accumulation of oil and gas in Kashi Sag, Tarim Basin, NW China

ZHAO Mengjun; WANG Zhaoming; SONG Yan; ZHANG Shuichang; XIAO Zhongyao; WANG Qinghua and QIN Shengfei

, 2005, 32(2): 1078-0.

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The most important source rocks in Kashi Sag, Tarim Basin, are Lower Carboniferous type Ⅱ marine sediment, Lower-middle Jurassic type Ⅱ-Ⅲ lacustrine Yangye Formation and the Lower Jurassic coal-bearing strata. The oil-gas-source correlation suggests that the oil seepages found in Kelatuo, Yangye, etc., was derived from the Middle Jurassic Yangye Formation, and the gas in Well Ake 1 was derived from the Lower Carboniferous. The pool filling process expressed that the pool accumulated the gas from Carboniferous source rock at a stage with high Ro value of 1.5%-1.8％. This is the major reason for the heavier gas isotopic composition. The oil derived from Jurassic source accumulated in Early Pliocene and was destroyed to form oil seepages and oil sand on surface.

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Thrust tectonics and hydrocarbon accumulation

HE Dengfa and JIA Chengzao

, 2005, 32(2): 1079-0.

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Reverse or thrust faulting is one of the main deformation styles. Remarkable progresses on fold-and-thrust belts have been made in recent years as follows: ① formation mechanism of the fold-and-thrust belts, and the dynamic interaction between surface processes and fold-thrust belt evolution; ② role of basement involvement and the contractional reactivation (inversion) of preexisting extensional faults in many thrust belts, the coupling between basement involved deformation and the sediment cover thin-skinned deformation; ③ mechanisms of fault-related folding and growth strata architectures as indicators of timing and mechanisms of folding; and ④ role of thrusting in the key factors of oil and gas pool formation, and the control of thrusting upon the distribution of oil and gas pools or fields. Many thrust-and-fold belts are combinations of both thin-skinned thrusting and basement-involved thrusting as a result of reactivation of preexisting extensional faults. Many fault-related folds appear to be hybrid structures involving changes in their deformation mechanisms through time and changes in their kinematic evolution. Recognition of the importance of detachment folding, limb rotation, and growth-strata geometries advances the understanding of thrust-belt folds. It resulted in the much more favorable association of pool formation factors in space, and much more important the best timing of the processes of pool formation, which give rise to lots of oil and gas fields in a large size. The different structural style and kinematics in the fold-and-thrust belts has primarily led to the change in the hydrocarbon fairways and enrichment of large oil and gas fields.

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Fault break-slope and low-stand fan sequence in Dongying Sag

SUI Fenggui; GUO Yuxin; WANG Baoyan and CAO Jianjun

, 2005, 32(2): 1080-0.

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Based on the bore section, combining with the study on lithology, well logging, seismic facies and sequence type, the structure of the sequence in the deeply down-faulted Dongying Sag is analyzed emphasizing on the low-stand fan depositional type, its controlling factors and depositional sequence. Results suggest that the low-stand fans have a relationship with the fault break-slope. The type, scale and location of the fault break-slope controls the low-stand fan distribution, which results in the forming of the typical abrupt slope-type and gentle slope-type low-stand fan depositional sequence. On the abrupt slope, under controlling of the boundary fault of limited back-off or continuously down, the low-stand fans of alluvial fan, fan delta, inshore under-water fan and turbidity fan are subsequently developed from border to center of the depression. On the gentle slope, low-stand fans of incised channel filling, braided delta, delta fan and turbidity are subsequently developed from border to center of the basin under controlling of the fault break-slope.

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Non-seismic techniques for oil and gas exploration in China

WEN Baihong; YANG Hui and ZHANG Yan

, 2005, 32(2): 1081-0.

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With the increase of observation precision of non-seismic equipments and the progress of data processing in ten years, non-seismic exploration techniques have been gradually used in 13 oilfields of PetroChina. Good social and economic benefits have been achieved. Based on these technique advances and exploration results, several examples in structural study and stratigraphic trap recognition are introduced. From reviewing the researches and applications, four development trends of non-seismic techniques are forecasted as 3D high-precision non-seismic exploration; non-seismic oil/gas prediction; non-seismic reservoir characterization and monitoring; and integrated exploration and joint processing.

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Key exploration techniques for the Lower Paleozoic carbonate buried-hills, Shengli Oilfield

MA Lichi

, 2005, 32(2): 1082-0.

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The relative simple and shallow carbonate buried-hill reservoirs have almost been completely explored after 40 years exploration, and deeply buried targets become difficult projects in Shengli Oilfield. The exploration techniques, such as trap description, reservoir prediction, recognition and protection are developed based on 3D prestack depth migration, FMI, pattern recognition and mating wellbore techniques. With the new techniques, Futai Oilfield and hundred million ton oil-bearing area Zhuanghai have been discovered and developed, which brought a breakthrough to the exploration in Bonan deeper buried-hill reservoirs.

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Micro-seismic monitoring on direction change of hydro-fractured cracks

LIU Jimin; LIU Jianzhong; LIU Zhipeng; ZHU Gangqin and WANG Lifeng

, 2005, 32(2): 1083-0.

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The whole hydraulic fracturing process of 7 layers in 3 wells of Chaoyanggou Oilfield, Songliao Basin, was monitored with a micro-seismic technology. Obtained results are similar to producing performance. Three representing mechanisms of crack direction change were discovered during the monitoring: ①two different direction cracks by different control factors changed direction obviously after fracturing; ②for the cracks with different initial direction controlled by the same factor, the crack changed to original direction in extension; ③cracks under the same factor may change direction with small angle. Three criteria to judge the crack direction change are introduced: ①crack direction and form is different; ②the second hydro-fracturing pressure is higher; ③ the new fracture does not extend along the original one, and the height may also be different.

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Niche genetic algorithms applied in inversion of pore media

BAN Shuhao and YANG Huizhu

, 2005, 32(2): 1084-0.

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In order to quicken the search for oil and gas in complicated underground media, the niche multi-parameter inversion algorithm based on EMPM (equivalent model of porous media) and seismic CT is proposed for porous media full of single-phase fluid. The algorithm integrates EMPM theory, Radon transformation and niche genetic algorithm and connects received signals with genetic colony. The theoretical analysis and inversion results indicate that the method can effectively avoid sophisticated solution of wave equations. The solution is easy to derive with high accuracy and can settle the problem of strata imaging between wells.

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Carbonate cave identification by using a spectral decomposition technique

CAI Rui

, 2005, 32(2): 1085-0.

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Ordovician carbonate reservoir consists of fracture and cave eroded by karstification. The various configurations, irregular spreading and lithologic heterogeneity, etc, increases the difficulty in reservoir prediction. The carbonate cave identification method using a spectral decomposition technique is introduced, taking advantage of the sensitivity of seismic frequency band to carbonate porosity, combining the abundant amplitude of the 3D tuning cubes and phase information with well testing, drilling and coring data. The method can be used to predict the inhomogeneous carbonate reservoir, and clearly reveal the fracture-cave distribution. The application of the spectral decomposition technique in identifying the fracture-cave in the Ordovician marine carbonate, west China, approves the effectiveness of the method.

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Operation characteristics analysis and process parameters selection of air drilling

SU Yinao; ZHOU Chuan and DOU Xiurong

, 2005, 32(2): 1086-0.

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Taking the compressed air as circulated fluid, air drilling has many different characteristics from mud drilling, such as pressure distribution, selection of drilling equipments and the reasonable configuration of drilling parameters. On the basis of the existing theory of air drilling, the new pressure model is constructed and calculation formulas are derived to get the distribution law of the pressure, the velocity characteristics of the compressed air, the variation of rotary speed of PDM(positive displacement motor) under the effect of temperature and pressure and the effect of temperature model variation on the pressure distribution in the circulation system. The calculations of minimum gas flow rate and reasonable ROP show that the increase of the flow section may result in the increase of minimum gas flow rate, and the most difficult position to carry cuttings in the hole is the turning point from small flow section to large flow section. And the reasonable ROP at flow rate of 1.2m3/s is obtained.

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Reservoir simulation of remaining oil distribution based on time-variant reservoir model

JIANG Hanqiao; GU Jianwei; CHENG Minfeng and SUN Mengru

, 2005, 32(2): 1087-0.

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Long-term water flooding would result in the variation of reservoir characteristics and crude properties. The time-variant model of unit 74-81 of Region 2, Shengli Oilfield, with reservoir characteristics and crude properties varying with the development of the unit, is established and the influence of development stage on remaining oil distribution and development efficiency is studied with reservoir simulation. The result shows that variation of permeability, crude viscosity and density, especially the variation of crude properties, strongly influences remaining oil distribution and recovery. The fine reservoir simulation of the unit 74-81 is carried out to determine the remaining oil distribution and water-out situation.

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Influences of gas recovery rate and aquifer size on production of sandstone water-drive gas reservoirs

SHENG Ruyan and LI Xiangfang

, 2005, 32(2): 1088-0.

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Numerical simulation of Fault Block Yong'an is carried out to study the influences of gas recovery rate and aquifer size on production performance of bottom-water drive sandstone gas reservoir. Results prove that traditional material balance equation is only applicable under conditions of low gas recovery rate and big aquifer size, and p/Z-Gp plot could be downward-curve when gas recovery rate is high and/or aquifer size is small. The p/Z-Gp plot may be a straight line under conditions of certain gas recovery rate and aquifer size, which is inconsistent with conventional understanding and indicates that judgment of drive type for a gas reservoir relying on p/Z-Gp plot alone may result in improper conclusion. When a gas reservoir produces under economically rational gas production rate, quite an amount of gas production will have to be recovered during water cut period.

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DST slug well test for low velocity non-Darcy flow in dual-permeability reservoirs

HUO Jin; JIA Yonglu and JIANG Weijun

, 2005, 32(2): 1089-0.

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The mathematical model of effective well radius for non gusher wells in DST slug well test of two layered reservoirs has been educed. Using Laplace transformation and Green Function method, the analytical solution of the model in Laplace space is obtained and new type curves is plotted for well test. The parameter sensitivity indicates that the change of the threshold pressure gradient, the storativity ration between layers and formation capacity ration will greatly influence the type curves. This is the main distinctive difference between Darcy flow and low velocity non-Darcy flow. Some important parameters such as the threshold pressure gradient, permeability and skin of separate layer can be obtained by using this model of DST slug well test analysis.

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“Apparent porous medium” identification and establishment in the Ordovician carbonate reservoir, Jingbian Gas field, Ordos Basin

XU Wen; LU Tao and CHEN Fengxi

, 2005, 32(2): 1090-0.

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Porous medium is the main storage space of Ordovician MW1 carbonate gas reservoir, Jingbian gas field, Ordos Basin. The fracture network of the major productive formations MW12 and MW13 only works for connecting pores. Well test results approved the storage and percolation characteristics of porous medium with limited conductivity. An "apparent porous medium" model is introduced to describe this kind of reservoir. The permeability contrast between core analysis and log interpretation is used to evaluate reliability of parameters, and the average core parameter is taken as the expectation value to constrain the model generation of parameter field, which could avoid the error from log interpretation, and only the integration contour line is weighted to perform the parameter field. The parameter field can correctly reflect the characters of the reservoir and reduce greatly the correction work of modeling parameter field.

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Single well microbial treatment technology and the effect of field application

JIANG Yan; XU Dengting; CHEN Jianbin; YUE Shenghui and SUN Yuzhi

, 2005, 32(2): 1091-0.

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Based on the components of waxy oil and conventional heavy oil, the groups of microbe F18 and F16 were selected, in which F18 has the ability to inhibit the deposition of the waxy components, and F16 has the ability to reduce viscosity of the heavy oil. The results show that F18 can degrade the long-chain aliphatic hydrocarbon which contribute to the deposition of wax, and produce bio-surfactant. The percentage of waxy components of oil and the solidification point are all decreased. F16 can reduce non-hydrocarbon components and produce bio-surfactant; thereby the mobility of oil is increased. The ratio of oil viscosity reduction is 30%-85% when oil viscosity is 50-3000 mPa·s (50℃). The microbial method has been used in 696 wells. The oil production has been enhanced significantly in these wells and the accumulated incremental oil production has amount to 72843.5t, with average incremental oil production of 104.66t per well. The hot washing cycle is lengthened or completely replaced by the new method, and the chemical usage is also decreased.

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Microbial flooding in Guan 69 Block, Dagang Oilfield

WANG Xueli; CHEN Zhiyu; LI Xiaoliang; LU Yongping; ZHANG Shiming; LI Xiulan; NI Jinzhong and DUAN Guanqing

, 2005, 32(2): 1092-0.

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With water cut rising up, the effect of water flooding on the recovery of the Guan 69 fault-block in Dagang Oilfield became worse. The same amount of microbaterial seeds is injected in each of the 4 injection wells. The DG002 and N80 with special effect on gel is used in the front plug, the N80 is applied in the main and the final plug. Two of the 4 testing well groups got better effects with slower yield decline and stable production performance. The yield of guan 69-8 is up to 23.3 t/d from original 21.88 t/d and the water cut of the Guan 69-21 decrease to 93.7% from original 95.6%.

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Laboratory investigation of CO2 flooding

HAO Yongmao; BO Qiwei and CHEN Yueming

, 2005, 32(2): 1093-0.

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In order to investigate the mechanism of CO2 flooding and provide project data, the phase behavior, viscosity reduction and slim tubule tests were taken to measure the PVT phase behavior of reservoir fluid-CO2 mixture, estimate the viscosity reduction effect of CO2 and disclose the mechanism of CO2 flooding. A method to get eligible reservoir fluid samples is proposed as mixing oil and gas samples to reach the bubble point pressure. Slim tubule tests indicate that it was more appropriate to determine the minimum miscibility pressure through the curve change of oil recovery with flooding pressure. The minimum miscibility pressure of the test, using the oil and gas samples of Shengli Oilfield, was 26 MPa. The tests and literatures show that for a certain reservoir, through a slight manipulation of the measured PVT properties including bubble point pressure, volume factor, swelling factor, solubility of CO2 and viscosity, it is possible to obtain single property curves, which can be used to estimated the PVT behavior for any fluid-CO2 mixture of this reservoir.

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Micro-mechanism and mathematic description of chemical flooding in heavy oil reservoir

WANG Zhuofei; LANG Zhaoxin and HE Jun

, 2005, 32(2): 1094-0.

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The emulsion flow in the porous media is a complicated and stochastic process. Droplets with different diameters reside and gather in the pores with different sizes, and break and separate in pore throats with different sizes. According to the mathematic description of the emulsion droplet diameter, the mathematic relationship between droplet diameter and capillary number and permeability is analyzed by micro-physicochemical hydrodynamic method. The probability distribution curve of droplets with different diameters is obtained combing the droplet distribution with capillary number, together with the pore throat distribution. The conditions for the break and separation of the droplets are also studied, indicating that reducing interfacial tension and improving capillary number can improve exploitation effect of the heavy oil reservoir.

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Resistivity drop mechanism during heavy oil thermal recovery

YANG Chunmei; LI Hongqi; ZHANG fangli; GAO Zhujun and LIU weidong

, 2005, 32(2): 1095-0.

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Reservoir resistivity falls obviously in adjustment wells during thermal recovery. The formation mechanism of large waterwetting channels and their influence on reservoir electrical properties was analyzed based on the basic sedimentary theory and tortousity parameters. Reservoir heterogeneity and hot steam breakthrough is the main reason for anisotropic electrical properties. The normal-resolution logging instruments are sensitive to the low-permeability zones in anisotropic formations, which results in the obvious decrease of resisitivity. The low resistivity of the adjustment wells cannot reflect real saturation of the output zones, but it offers information for the study of steam breakthrough rules, reservoir evaluation and development adjustment.

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Low damage fracturing technology for explo-ration wells in low porosity and permeability reservoirs

YANG Bingxiu; JIANG Tingxue; DING Yunhong; WANG Yongli and WANG Shizhao

, 2005, 32(2): 1096-0.

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The evaluation of the characteristics of the formation may be incorrect because of the formation damage caused by improper fracturing design and treatment. In order to broaden the knowledge and evaluation of low porosity and low permeability formations, low damage fracturing technology is put forward on the base of comprehensive analyses of fracturing experiences in exploration zones as Tarim, Huabei, Jilin, Qinghai, Yumen and Changqing Oilfield, etc. The highlight of the new fracturing technology lies in laboratory test and analytical technique related to damage, development of low damage fracturing materials, low damage technology design method and low damage of corresponding measures. Well Lu-45 in the low porosity, ultra-low permeability and low resistance formation of Liuxi exploration zone, Huabei Oilfield, was hydraulically fractured using the new fracturing technology in year 2003, which brought the first breakthrough in Liuxi exploration zone for the past decades.

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Three standards for studying low-resistivity oil zones

LI Hao; LIU Shuanglian; WU Bofu and LIU Weixing

, 2005, 32(2): 1097-0.

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Under an extensional geological condition, low resistivity oil zone caused by high irreducible water saturation is formed in weak and unstable water dynamic areas where the change of water dynamic results in special reservoir lithological structure. The micro-pores and macro-pores make up the dual-porosity pore system. The resisitivity is low because of the high irreducible water saturation, but the macro-pores accumulate mobile oil and gas. Based on the three standards as reservoir microscopic structure, reservoir lithological structure and sedimentary facies distribution, the distribution of low resistivity oil zone can be forecasted by the research on sedimentary facies. Improved yield has been achieved in several wells of Dagang Oilfield.

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Numerical simulation of fracturing naturally-fractured reservoirs

LI Yongming; GUO Jianchun and ZHAO Jinzhou

, 2005, 32(2): 1098-0.

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Taking account of mass exchange between macro-fracture and matrix in the micro-fracture system, the multi-medium percolation model with macro-fractures is set up. The simulator for post-frac performance of naturally-fractured formation is developed. Using the data of Tahe fractured reservoir, the effects of natural fracture, artificial fracture and macro-fracture on post-frac productivity show that the permeability of the natural fracture is one important factor affecting post-frac productivity. The decrease of artificial fracture conductivity with time has important effects on post-frac productivity. Fracturing may lead to the damage of natural fracture. The increase of the length of artificial fracture can benefit fluid flowing to the well bottom along artificial fracture. But the increase of fluid leak off may result in serious damage of natural fracture. If the permeability of natural fracture is low with poorer-connecting, it is difficult to acquire better fracturing results. The post-frac production with macro-fracture is higher than that without macro-fracture.

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Water shut-off in deep producers in high temperature fractured reservoirs

ZHU Huaijiang; HE Fan; WANG Rongjun and ZHANG Xingui

, 2005, 32(2): 1099-0.

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Shixi Oilfield locates in the middle of Junggar Basin, with the characteristics of high temperature, high formation pressure, high salinity and water cone in ultra deep producers. Five oilfield tests of water shut-off showed that treatments to use an amphoteric ion polymer gel or an inorganic system of lime-cement as plugging agents could neither decrease water cut nor increase oil production. Producers could be shut-off with inorganic silica gel-polymer gel seal, or with pre-crosslinking swellable granules made from plant fiber-polymer gel seal, which resulted in output decrease of both oil and water. In order to ensure that plugging agents selectively enter water bearing formation to form barrier without pay zone damage, it was required to adjust plugging agent system and improve injection process. A three slug technique, in which a temporary plugging agent, a main slug (surfited larch tannin extract) and the sealing cement were injected separately, was used successfully in a water shut-off pilot test in the faulted reservoir in Shixi Oilfield. Although the test brought out the purpose of decreasing water cut and increasing oil output, the better result would have been produced with a higher plugged radius. It was demonstrated that: success ratio of water shut-off in ultra deep producers in high temperature reservoirs could be boosted greatly if the reservoir and producer condition was clear, and plugging agent systems which could selectively seal the water bearing formation and an improved injection technique were used.

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Mechanism evaluation of condensing/vaporizing miscible flooding with hydrocarbon-rich gas injection

TANG Yong; SUN Lei; ZHOU Yongyi; LI Shilun; SUN Liangtian and DU Zhimin

, 2005, 32(2): 1100-0.

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Based on the EOS and the phase equilibrium theory of oil-gas systems, the calculation models for pressure-composition experiment and multi-contact miscible experiment of gas injection were built. And a systemic evaluation method was proposed,which applies the existing work tools (component simulator) to simulate the PVT experiment data, pressure-composition experiment, multiple contact miscible experiment and slim-tube experiment available to evaluate the miscible ability and mechanism of gas displacement. The miscible mechanism of hydrocarbon-rich gas injection in Qiulin Oilfield, Tuha Basin, was evaluated. The results approve the existence of the combined condensing/vaporizing mechanism in hydrocarbon-rich gas displacement and show that the evaluation method by extending the experimental data presented here can provide a reliable theoretical basis for the design of miscible gas injection project in oilfield. The recovery under relatively low interfacial tension, i.e, near miscible flooding, is near to that of miscible flooding.

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, Volume 32 Issue 2