Petroleum Exploration and Development

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Petroleum exploration progresses during the 10th FiveYear Plan and key exploration domains for the future in China

ZHAO Wenzhi; HU Suyun; DONG Dazhong and YU Yuanjiang

, 2007, 34(5): 1512-0.

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During the 10th Five-Year Plan, exploration investment for hydrocarbons had been increasing. Great progresses were made on the exploration of lithologic-stratigraphic reservoirs in continental lacustrine basins. There were successive significant discoveries in the foreland thrust belts in western and central China. Outstanding achievements were from the middle and lower combinations of superimposed basins. Precise exploration turned out to be a productive tool in mature basins. The offshore discoveries were tremendous. By the end of the period, oil exploration was steady, and gas exploration was growing rapidly. The hydrocarbon reserves growth was in a new peak stage, and the reserve/production ratio was improved markedly. During the 11th Five-Year Plan, the hydrocarbon exploration will be developing rapidly. New discoveries will emerge unceasingly in seven domains: hydrocarbon-rich sags in rift-subsidence basins, large lithologic-stratigraphic reservoirs in huge depression basins, marine carbonates, large cratonic palaeohighs, foreland thrust belts, offshore deepwater, and unconventional oil and gas resources.

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Main controlling factors and mode of natural gas accumulation in Bohai Bay area

XUE Yongan; LIU Tinghai; WANG Yingbin; ZHANG Guoliang and WEI Zhonghua

, 2007, 34(5): 1513-0.

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Based on the comparison of oil-rich and gas-rich sags in the Bohai Bay basin, two main controlling factors of gas reservoir-forming are summarized: gas-rich sags have source rock of partial humic or high maturation sapropel type; thick abnormal pressure mudstone in lower Tertiary is the cap, or "quilt". Five main reservoir-forming models are concluded: "under quilt" model A, namely new generation, new reservoir, new cap; "under quilt" model B, namely new generation, old reservoir, old cap; "in quilt" model, gas pools are inside abnormal pressure mudstone; "above quilt" model A, gas migrates upwards along transport layers and faults, accumulates in shallow layers, and forms small gas reservoirs; "above quilt" model B, the "dry gas" formed by degradation of crude oil in shallow heavy oil fields collects above the field. Among them, the "under quilt" model has the highest fill factor and reserves. The north subsag of Liaozhong sag and the Bozhong sag have great gas potential.

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Prediction of Liwan deep submarine fan sand body distribution, Baiyun Sag, Pearl River Mouth Basin

ZHENG Xiaodong; ZHU Ming; HE Min; LI Hongwei; LIAN Shiyong and ZHANG Xin

, 2007, 34(5): 1514-0.

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A deep submarine canyon and turbidity channels were developed along the hanging wall of faulting break zone as a result of the 13.8Ma regression. The deep submarine fan was developed in the footwall near the outlet of the canyon. According to the seismic response characteristics, the fan is characterized by the progradation reflecting seismic facies parallel to the direction of paleocurrents and by the mounds reflecting seismic facies perpendicular to paleocurrents. The fan can be divided into three period overlapping lobes based on the prograding sequence relationship. Based on the seismic facies analysis, the sand body distribution of the fan is predicted. During the development of the fan, coarse fragments unload firstly near the footwall of the faulting break zone due to gravitation, and fine-grained sediments are taken in suspension to and deposit in the edge or further areas, so the main part of the lobes is rich in sand and their edges and front ends are rich in mud.

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Controlling factors of reservoir ability of Carboniferous and Permian coal rocks, North China

JIN Zhenkui; WANG Chunsheng; WANG Pu and ZHANG Yanlong

, 2007, 34(5): 1515-0.

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The reservoir ability of coal rocks is controlled by both sedimentary facies and diagenesis. Sedimentary facies controls the content of ash and macerals, which affect the reservoir ability of coal beds. There exists a quantitative relation between ash production rate and porosity and permeability of the coal. The more the ash, the lower the porosity and permeability. Vitrinite is favorable to the formation of cleats. The higher the vitrinite content, the higher the porosity and permeability. From dull coal to bright coal, vitrinite tends to increase, ash tends to decrease, and porosity and permeability tend to increase. In the study area, coals were deposited in tidal flat and delta environments. Coals formed in tidal flats show higher porosity and permeability than those formed in deltas, and those formed in lower delta plains higher than those formed in upper delta plains. Due to denudation, coal rocks in the vadose and phreatic zones show better reservoir ability, while deeply buried coal beds, due to cementation and compaction, show poorer reservoir ability.

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Genesis of reef flat body matrix secondary pores in Upper Ordovician in central area of Tarim Basin: A case from Well 62 field of Central Tarim

SUN Yushan; HAN Jie; ZHANG Lijuan and TAN Zejin

, 2007, 34(5): 1516-0.

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Through several microanalysis methods under microscope, the genetic mechanism of reef flat matrix secondary pores in the Ordovician Lianglitage Formation in No.1 structural belt of Central Tarim Basin was traced and analyzed according to diagenetic evolutionary series. The matrix secondary pores are generated in the middle diagenetic stage under the middle-deep buried condition, which is associated with high-temperature and high H2S content solution caused by TSR from the deep section. The solution enters along faults and fracture zones and corrodes reservoirs, and the corroded components are algal grains (or algal cement) bearing micritic limestone arene and filtrational silts. As a result, the matrix secondary pores are generated in types of intragranular dissolved pore, foundry pore and intergranular dissolved pore. Grain beaches in platform margins, reef flanks and hillocks are abundance zones for soluble components and favorable belts for generating matrix secondary pores. The development zones of fissure systems in these areas are potential for high-quality reservoirs.

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Physical properties and exploration and development potential of coalbed gas reservoirs in Yangjiaping, Liulin County, Shanxi Province

YAO Huifang

, 2007, 34(5): 1517-0.

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In order to confirm the exploration and development potential of coalbed gas in the Yangjiaping experimental area, Liulin, this paper studies the important reservoir characteristics of the main coal beds in the area, such as coalbed cleat, porosity and permeability, and the important production parameters, including gas content, gas saturation, and adsorption/desorption time by observation, experiment, and production data analysis. The coalbed gas reservoirs consist mainly of matrix pores. The coalbed permeability varies greatly and the main coalbeds usually have lower permeability. The coalbeds have developed irregular reticulated cleats. The cleats are dominated by regional structures and most of them are open, and thus having good permeability. The coalbeds have a higher gas content (nearly saturated) and good exploration potential. The coal had a short desorption time, showing favorable exploitation conditions. The production data of coalbed gas wells also confirms the excellent exploitation potential of the area.

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Geochemical characteristics of seepages and their source in Majiashan of Chaoxian， southern Anhui

SONG Huanxin; XIAO Tianjun; WEN Zhigang and ZENG Yantao

, 2007, 34(5): 1518-0.

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Oil seepages of Majiashan in Chaoxian south of Anhui province mainly appear in the T1n Formation. To determine their source rock, the Mesozoic and Paleozoic marine source rock in the area was studied and calibrated accurately based on the detail data of field profiles and sampling records. Source beds rich in organic matter have been discovered in the P1q, the P2d and the T1n. The fingerprint characteristics and absolute concentration of biomarkers indicate that the distribution and composition characteristics of tricyclic terpanes, tetracyclic terpanes, triterpanes, sesquiterpanes, and steranes of samples from T1n are similar to those of the oil seepages. The absolute concentration of hopanes, tricyclic terpanes and steranes of oils from T1n is also similar to the seepages. However, there are significant differences between the oil seepages and the samples from the P1q and P2d. The Majiashan oil seepages have genetic relationship with the T1n source rock and are the original oil of T1n.

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Relationship between faults and hydrocarbon accumulation in Panyu low massif and north slope of Baiyun Sag, Pearl River Mouth Basin

YU Shuiming; MEI Lianfu; SHI Hesheng; QIN Chenggang and TANG Jiguang

, 2007, 34(5): 1519-0.

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The relation between faults and hydrocarbon accumulation is researched by the analysis of fault classification, activity history, and petroleum charge history in the Panyu low massif and the north slope of Baiyun sag. Two kinds of faults including long active fault and late active fault exist in the area. The active periods of these two kinds of faults matched the periods of hydrocarbon charge, so they should have acted similarly in hydrocarbon charging. Exploration results and ample evidence show that faults are the main passage for oil and gas migrating vertically and the hydrocarbon accumulation is controlled in Neogene by current static fault sealing in which the main control factor is lithologic juxtaposition. The research about the evolvement of target layers, traps and fault-seal should be strengthened and the traps which are in the path of petroleum migration and have static fault sealing are easier to be explored successfully.

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A quantitative method for appraising reservoir geological model uncertainty

HUO Chunliang; LIU Song; GU Li; GUO Taixian and YANG Qinghong

, 2007, 34(5): 1520-0.

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To improve the uncertainty appraisement of reservoir geological models, a quantitative appraisement method, using OOIP and drainable OOIP as the indexes and based on 3-D stochastic reservoir modeling, is put forward. Uncertainties of reservoir models exist in the process of modeling and in the calculation of reserves, and the uncertainties in facies modeling are focused on. Based on the modeling realizations of geological models which are singled out by experiments and designed to describe the likelihoods of reservoir characteristics, the effects of uncertainty factors on the modeling are estimated quantitatively and the statistic features of the main factors are figured out. Using the multinomial response surface of the main uncertainty factors and reserves as the substitute for modeling, probabilistic reserves are calculated by Monte Carlo method. Taking into account of reserve scale, reservoir connectivity and probability, a set of optimized realizations are provided to numerical reservoir simulation.

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Abnormal value recovery of maturity parameter Tmax for Rock-Eval

ZHANG Zhenling; WU Liyan; TUO Qi and SHU Nianzu

, 2007, 34(5): 1521-0.

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The Tmax values will be abnormally low when the source rocks are contaminated by soluble organic matters, such as oil, bitumen and the like. These organic contaminants can be removed by increasing the initial S2 pyrolysis temperature, and the normal values of Tmax can be got. Different initial S2 pyrolysis temperatures have been tested on both high maturity source rocks and low maturity source rocks, in which different organic matters such as non-hydrocarbon, chloroform extract, crude oil or additive in drilling fluids are contained. On the basis of the test results, it is proposed that the normal Tmax values could be recovered at the S2 pyrolysis temperature range of 380-600℃.A heavily contaminated source rock has been recovered by this method, the Tmax has best correlation with Ro of cuttings in well BXX.

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Early movable-gel-driving in water-flood development of heavy oil reservoirs

SONG Shemin; WANG Yazhou; ZHOU Jun and MENG Lixin

, 2007, 34(5): 1522-0.

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The Zhao 108 fault-block of Huabei Oilfield is a multi-layered ordinary heavy oil reservoir. During the water flood development, the oil production decreased seriously, the water cut increased quickly, the interlayer interference was obvious, and the water flood efficiency was low. In order to improve the effect of reservoir development, in the early stage of water flooding, the periodic movable-gel-driving, consisting of 4 rounds, was implemented, achieving an annual output of 30,000t for 10 years. In contrast to the simulated pure water flooding results, the 10-year development of early movable-gel-driving results in an oil recovery of 21% with an increase of 10.01%, a water cut of 67.6% with a decrease of 25.4%, and a much lower increased rate of water cut. Production of Zhao 108 fault-block shows that the oil recovery is increased with a longer period of stabilized production, a higher water utilization rate, a shorter investment recovery period, and a much better economic benefit.

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2-D physical modeling of water coning of horizontal well production in bottom water driving reservoirs

WANG Jialu; LIU Yuzhang; JIANG Ruyi and GUAN Changzhi

, 2007, 34(5): 1523-0.

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A 2D visible physical model of horizontal well production was set up using the advanced electronically monitoring technology and flow testing tools to investigate the fluid flow in bottom water driving reservoirs during horizontal well production. The formation and development of water coning were visualized, and the effect of water coning on water breakthrough times and recovery ratios was studied. When horizontal section is short, the water coning is formed in a short time, the two shoulders of the coning are steep and the oil/water interface deforms greatly. When horizontal section is long, the water coning is formed in a long time, the two shoulders of the coning are gentle and distributed symmetrically. With the increasing of horizontal section length, the water breakthrough time delays,the water free recovery and the ultimate recovery increase. The increase of producing pressure shortens the production period before water breakthrough, and decreases both water free recovery and ultimate recovery.

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A new method for calculating kickoff pressure gradient in low permeability reservoirs

XU Jianhong; CHENG Linsong; ZHOU Ying and MA Lili

, 2007, 34(5): 1524-0.

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The fluid flow in low permeability reservoirs does not follow the Darcy equation and presents non-linear fluid flow through porous medium due to the existence of kickoff pressure gradient. A series of displacement experiments are carried out by using 23 different permeability cores of the Changqing Oilfield. Based on the mechanism of fluid flowing through porous media, the data are treated, and a new physical model is presented. According to the regression and analysis of the data, a new mathematical model is obtained between the kickoff pressure gradient and driving pressure gradient and fluidity of low permeability formation. According to the mathematical model, the affecting factors of the kickoff pressure gradient are driving pressure gradient and fluid mobility, the kickoff pressure gradient is in direct ratio to driving pressure gradient and in inverse ratio to fluid mobility. Theoretical plates between the kickoff pressure gradient and its affecting factors of low permeability reservoirs are attained.

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Model of gas saturation determination based on elastic modulus

WANG Caizhi and ZHANG Lijun

, 2007, 34(5): 1525-0.

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The quantitative determination of gas saturation based on elastic modulus can improve the ability of reservoir evaluation from well logging. Once the velocities of compression and shear waves are obtained from dipole acoustic-array logging data, the elastic moduli can be determined. According to Gassmann equation which describes the relationship between bulk modulus and shear modulus in a low frequency situation, an equation is established between the gas saturation and bulk modulus as well as shear modulus in the cases of gas saturated, water saturated and dry clay separately, from which the model of calculating gas saturation based on acoustic modulus is derived and a software is developed. The good result of in situ data process and interpretation with the aid of the software is verified by the oil test and mud logging data.

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Effects of fresh drilling mud invasion on logging responses of dual induction and dual lateral to reservoirs

LI Changxi; LI Chaoliu; ZHOU Cancan; OUYANG Jian; XIU Lijun and SHI Yujiang

, 2007, 34(5): 1526-0.

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The invasion of drilling mud can cause the radial variation of reservoir parameters such as water saturation, salinity of formation water and formation resistivity etc. The effects of radial variation of formation resistivity on the logging responses of dual induction logging and dual lateral logging to reservoirs are different due to their different measuring principles. Statistics of measured data and numerical simulation results verify that the increased resistance invasion of fresh mud exerts more influence on dual lateral logging in water formation and the decreased resisance invasion of fresh mud does more influence on dual induction logging in oil formation. Methods of identifying water or oil formation applying dual induction logs or combination of dual induction logs and dual lateral logs are established for low resistivity oil reservoirs according to the effect differences of fresh mud invasion on the responses of dual induction logging and dual lateral logging to reservoirs, and the corresponding evaluation method of oil saturation is also established.

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Streamline numerical well-testing interpretation model for multilayered reservoirs

WU Minglu and YAO Jun

, 2007, 34(5): 1527-0.

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A streamline numerical well-testing interpretation model for multilayered reservoirs is presented based on the streamline method and the numerical well-testing theory. The model consists mainly of two mathematical models, one for the production period and the other for the testing period. The former is actually a black oil model while the latter is a streamline model composed of all the mathematical equations established for each streamline traced from testing wells. All of the models can consider various influential factors (such as commingled production/injection, producing history, heterogeneity, multi-phase flow, multi-well interference, interlayer interference and so on) and be solved by the streamline method, which ensures the high calculation speed and reliable stability and thus setting a good basis for the auto-matching interpretation of numerical well-testing data. The validity of the model is proved by solving an ideal multi-layered reservoir and analyzing the model features.

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Apparent viscosity model of power law fluid flow in heavy oil wells

LI Yang; ZHANG Kai; WANG Yazhou and WANG Linna

, 2007, 34(5): 1528-0.

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The viscosity of liquids produced from heavy oil wells is higher than that from regular oil wells. It causes problems in the process of heavy oil production, such as low pump efficiency, high changeability of suspending loads, and the difficulty in adjusting parameters. To solve the problems, rheology of heavy oil from 5 wells in the Shengli Oilfield is researched through experiments under 35-100℃ as to the whole process of artificial lift. Experimental formula regressed by the power-law model shows the relationship that power-law index and consistency coefficient vary with temperature. According to different flow rules from bottom hole to wellhead, equations of motion and boundary conditions in vertical well-bores are set up on the basis of the non-Newtonian fluid rheology and artificial lift theory. A model of apparent viscosity is put forward by solving above equations. The application result shows that this model is conducive to improve design precision of rod-pumped wells with heavy oil.

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Anti-sloughing mechanism of silicate drilling fluid and its application technology

XU Jiafang; QIU Zhengsong; Lü Kaihe and YU Lianxiang

, 2007, 34(5): 1529-0.

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The microscopic anti-sloughing mechanism of silicate drilling fluid is explored by using advanced experimental apparatus and reseach approaches such as Zetasizer 3000 potential & granularity meter, Turbiscan infrared dispersion steady indicator and SHM (the simulation equipment of hydra-mechanics coupling of shales). The granularity distribution of silicate water solution of 5 percent concentration is narrower and deeply affected by the silicate module and pH, the grains are even, and the optimum amount of the cooperation inorganic salt is 3 percent. The Zeta potential of silicate colloidal solution, which can stablize the dispersion system of claystone bit cuttings, ranges from －41.0mV to －31.0mV. The reaction of silicate with shales can buildup a compact isolate membrane to block or postpone the invasion of mud filtration and the pressure transmission. One silicate drilling fluid formula is developed, and field tests demonstrate that the drilling fluid has good rheology and a strong rejection capability.

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Two ways for breaking out and forecasting stimulation production by production composition method

BIE Aifang; JI Guang; ZHANG Xiangyang; FENG Mingsheng and QU Debin

, 2007, 34(5): 1530-0.

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Two methods are proposed for breaking out and forecasting the stimulation production of certain bulks of oil wells (reference bulks and track bulks) from a developmental unit's historical production data. The steps are: deciding the analogy objects and their parameters to be analogized, breaking out production compositions based on the whole production data during the past years and the production data of individual wells that are put into production in those years, achieving the quantitative forecasting models of the reference bulks' stimulation production through regressing, and then forecasting the track bulks' stimulation production by analogy. Method One uses the reference bulks' stimulation production as regression variables and directly calculates the track bulks' stimulation production in the following years; Method Two uses the reference bulks' total production rate and their natural production rate as regression variables and then indirectly calculates the track bulks' future stimulation production. Method Two has theoretical base, and is more reliable than Method One in predicting stimulation production of track bulks from a developmental unit in the decline period.

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Reservoir formation and oil and gas distribution of Fula Oilfield, Sudan

YU Chao; BAI Yang; YU Zhongyang and YU Zhongliang

, 2007, 34(5): 1531-0.

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Fula Oilfield in the Fula sag is one of the main petroleum-producing areas in the Muglad basin. The Fula sag suffered three faulted depressions in Early Cretaceous, Late Cretaceous and Tertiary. AG shale formation deposited in the first depressed period is the main hydrocarbon source, and Aradeiba, Bentiu and upper AG Formations are the main oil-bearing series; reverse fault block (nose-type) is the leading trap; the big fault cut into the AG Formation is the main channel for migration vertically; the lateral sealing of shale in Aradeiba Formation is the key control factor in forming the Aradeiba and Bentiu reservoirs; the successively developed palaeohigh in the AG Formation is the favorable hydrocarbon concentration area, the effective lateral and vertical seals by the shale in the upper section of AG are the crucial factors for the AG reservoirs. Aradeiba Formation is a single bedded reservoir; Bentiu Formation is a reservoir with complex oil-water distribution and tilted oil/water interfaces; AG Formation is a layered reservoir with multiple water/oil/gas systems vertically.

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, Volume 34 Issue 5