Petroleum Exploration and Development

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Geological features and evaluation techniques of deep-seated volcanic gas reservoirs, Songliao Basin

ZHAO Wenzhi; ZOU Caineng; FENG Zhiqiang; HU Suyun; ZHANG Yan; LI Ming; WANG Yuhua; YANG Tao and YANG Hui

, 2008, 35(2): 1578-0.

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The significant breakthrough of natural gas exploration in deep-seated volcanic rocks of Songliao Basin demonstrates that volcanic rocks as reservoirs can form natural gas accumulations where excellent source-reservoir-seal associations exist. This paper reveals several features of volcanic gas accumulations: (1) Two types of reservoirs including hydrocarbon and non-hydrocarbon are developed, the former is organic and usually trapped in shallower volcanics associated with sub-deep-seated faults, the latter is mainly inorganic and accumulated in deep-seated volcanics associated with large-scale deep-cut basement faults. (2) The Lower Cretaceous Shahezi coal series source rock, Yingcheng volcanics and Denglouku mudstone form good source-reservoir-seal associations, which control the major volcanic plays. (3) Volcanic crater and eruptive facies spread along deep-seated faults, so discordogenic faults control the distribution of larger-scale volcanic gas reservoirs. (4) Fracture zones, accompanied with large-scale faults, control the distribution of high-yield zones. (5) Effusive volcanic rocks in deep part of sags have huge thickness and contact extensively with source rock, so the gas accumulation potential is promising if reservoirs exist. Evaluation techniques can be summarized into three steps: (1) Determining of volcanic rocks distribution by joint inversion of gravitational, magnetic and seismic data; (2) Predicting the distribution of volcanic reservoirs by multiple methodologies; (3) Prediction on distribution of gas-bearing volcanic rocks by integrated methods including gas detention.

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Dynamic conditions of Mesozoic petroleum secondary migration, Ordos Basin

LIU Xinshe; XI Shengli; HUANG Daojun; ZHANG Qing and WANG Xin

, 2008, 35(2): 1579-0.

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Tectonic movement of the Ordos Basin is characterized by the whole ascending and descending. The main driving forces of petroleum migration in the Mesozoic are buoyancy and abnormal pressure. The continuous oil column height in reservoirs of the Jurassic Yan'an Formation is close to the calculated oil column height required to overcome capillary pressures. The width of the discovered oil-bearing belt below the Tertiary Yanchang Formation is far less than that needed for overcoming capillary pressures. Study of the mudstone compaction curves of more than 100 wells reveals that the driving force was buoyancy in the Jurassic and the upper part of Tertiary Yangchang Formation, and during the period of large quantity petroleum accumulation, middle and lower reservoirs of the Yangchang Formation were very tight, the formation basically lost water alternating ability, and the extensively developed abnormal high pressure became the main dynamic force of petroleum secondary migration.

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Changxing Formation biohermal gas pools and natural gas exploration, Sichuan Basin

CHEN Zongqing

, 2008, 35(2): 1580-0.

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Plain fluvial facies, paralic facies, shallow gentle slope facies on carbonate platforms, platform marginal reef facies, Kailiang trench facies, and northern Sichuan-western Hubei ocean basin facies are developed in the Permian Changxing Formation and have favorable source-reservoir-seal conditions. To improve the seismic prediction reliability of biohermal anomalies, an identifying model of biohermal seismic anomalies was established in late 1990s based on the geological features of known reefs and the corresponding seismic reflection features, and 182 biohermal anomalies were found in eastern Sichuan. Researches on sedimentary facies reveal a platform marginal reef facies from both sides of the Kailiang trench to west Hubei, and the seismic anomalies of 36 marginal reefs have been found there. These marginal reefs have large areas and high drill proved reserves. The facies belt is likely to extend to the western margin of the basin. Many point reefs are developed on the slope platform facies, and 146 seismic anomalies of point reefs are found in eastern basin. Point reefs are possibly developed widely in central basin.

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Hierarchical division and origin of single sand bodies in Fuyu oil layer, Fuyu Oilfield

ZHANG Qingguo; BAO Zhidong; SONG Xinmin and SUN Jiwu

, 2008, 35(2): 1581-0.

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During the middle and late periods of water-flood, three-dimensional distribution and connection of single sand bodies in reservoirs are important research issues. Based on core analysis and dense well logging, in combination with sequence stratigraphic and hierarchic analysis of reservoirs, the Fuyu oil layer was divided into 4 sand members and 13 sub-zones. Two sedimentary sub-facies, 9 sedimentary micro-facies and 7 single-genesis sand bodies were identified. Four-type overlay models of combination channels were put forward by using sub-zone contrast technique and characteristic changing of well-logging responses. The single-genesis sand body boundary was identified. The average width and thickness of individual sand body is 150 to 500 meters and 3 to 7 meters, respectively. The average ratio of width to thickness is 40∶1 to 120∶1. Wider and thicker composite channels were developed by the cutting and folding of the sand bodies in delta-plain branch channels and delta-front sub-aqueous branch channels, and thus formed the best reservoirs of remaining oil.

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Fluid inclusions in reservoirs of Weixinan sag, Beibuwan Basin

LIU Ping; XIA Bin; TANG Zaiqiu; WANG Xiaoguang and ZHANG Yi

, 2008, 35(2): 1582-0.

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To make sure the petroleum migrating direction and pool-forming model in the Weixinan sag, 4 wells were chosen to do research on fluid inclusions and petrography. The petroleum inclusions have three types: type Ⅰ occurs in early cracks of quartz debris grains or the overgrowths inside, type Ⅱ in the margins or overgrowths of quartz grains, and type Ⅲ in late cracks of quartz debris grains. According to PVTsim, Ptr and Ttr are modeled and calculated. The results are: type Ⅰ is 97.9 ℃ and 19.13 MPa; type Ⅱ 112.6 ℃ and 35.05 MPa; type Ⅲ 157.4 ℃ and 47.52 MPa. Based on burial history, three fluid-charging events occurred about 33Ma, 26.5Ma and 7Ma ago, respectively. Migration directions and pool-forming models are: Fluid type Ⅰ migrated towards west-north and north-east respectively to form structural and lithologic reservoirs; Fluid type Ⅱ migrated to areas surrounding the sag and formed block faulted and buried hill reservoirs; Fluid type Ⅲ migrated to slopes to form anticlinal reservoirs.

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Developmental mechanism of advantageous Xixiangchi Group reservoirs in Leshan-Longnüsi palaeohigh

WANG Sufen; LI Wei; ZHANG Fan and WANG Xingzhi

, 2008, 35(2): 1583-0.

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The Leshan-Longnüsi palaeohigh in the Sichuan Basin controlled by basement uplift underwent multistage or multicyclic syndepositional uplifting and denudation uplifting during evolvement. Carbonate reservoirs are developed in the Lower-Upper Cambrian Xixiangchi Group in this area. The reservoirs are compact and have low matrix porosity and permeability. But porous and dissolution layers exist locally, and porous layers commonly occur in pinhole and coarse textural dolomites. Fracture growth may improve the reservoir penetration conditions. Karstification in the depositional and weathering stages is the main diagenesis of the reservoirs. The main developmental zones of excellent reservoirs are palaeo-karst crust of weathering and the area where karst ramps and structural fractures coexist.

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Upper Cambrian-Ordovician reservoir characteristics in Well Gucheng-4 area， Tarim Basin

ZHU Changjian; XIAO Zhongyao; ZHANG Baomin; JIN Yingai; SANG Hong; LIU Yongfu and DANG Qingning

, 2008, 35(2): 1584-0.

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Based on the data of regional geologic background, core and thin section, this paper studies the characteristics of sedimentary facies and reservoirs of the Upper Cambrian-Ordovician in Well Gucheng-4, Tarim Basin, and points out the potential and targets of petroleum exploration in the Gucheng break-slope. Collapsed breccias of platform margins are deposited in the Upper Cambrian, arenite and lime mud mound facies of shallow glacis of platform frontal-margin are deposited in the Ordovician Penglaiba, Yingshan and Yijianfang Formations, knollenkalk of deep-water glacis of platform frontal-margin is deposited in the Ordovician Tumuxiuke Formation, and slope-continental shelf-abyssal basin facies is deposited in the Ordovician Queerqueke Formation. The Upper Cambrian dolomite is a better reservoir which is controlled by deposition environment, dolomitization and structural fractures. The Ordovician limestone reservoir is poor because of most primary pores being filled by cementation. The favorable exploration targets are in the north and west of the Well Gucheng-4 area.

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Sedimentary and evolutionary characteristics of dereliction deltas in Chang 6 - Chang 2 oily members, Zhidan region, northern Shaanxi

WANG Jianmin

, 2008, 35(2): 1585-0.

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The study using well logging data and the sedimentological method reveals that large deltas and lake systems developed time and again in the Chang 6 - Chang 2 depositional stage in the Zhidan region, and a good intraplot source-reservoir-cap assemblage and widely spread oil-bearing series are formed. In sub-south-north cross-section, the Chang 6 - Chang 2 sedimentary association shows that deltaic deposits progressively overlapped lake deposits from bottom to top and from north to south, forming upward coarsening dereliction depositional sequences; sedimentary facies belts moved continually towards the lake center from north to south, deltafront subfacies spreaded extensively and overlapped in multiphases, forming the main intraplot depositional body. Deltafront subfacies may be subdivided into underwater distributaries plain and anterior margin river mouth subfacies, and the main sand bodies are river mouth sand bank and distributaries channel sand body; the Chang 6 stage's anterior margin river mouth subfacies in the region were well-developed; to Chang 2 stage, underwater distributaries plain subfacies extended and developed rapidly, and deltaic plain subfacies began to come into the region.

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Reservoir properties of Suderte buried hill and main controlling factors, Beir Sag， NE China

KANG Dejiang; PANG Xiongqi and ZHANG Yunfeng

, 2008, 35(2): 1586-0.

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From drilling data, core and thin section analysis, the sandbody of the Suderte buried hill is of low porosity and low permeability. After being reformed by late diagenesis, its reservoir conditions get better. Reservoirs around the Bei 2 well and the Beir town in the middle of the buried hill belong to the second level and have moderate reservoir capacity; reservoirs on its east and west sides are the third level and have poor reservoir capacity. Reservoir capacity distribution relates closely to the degree of fracture development and the late reforming and less to primary porosity and permeability. The reservoir’s effective spaces are mainly structural fractures, solution holes in cements, (dissolved) pores in particles and fractures. Reservoir capacity is affected by lithology, tectogenesis and diagenesis. The region that has brittle rocks with much fractures and much tectogenesis are prone to accumulate oil-gas, and strong compaction and cementation are important factors of destroying reservoir capacity.

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Petroleum geology and exploration of beach sandbar in Junggar Basin, NW China: A case from the Shawan Formation in Well Pai 2

XIANG Kui; BAO Zhidong and ZHUANG Wenshan

, 2008, 35(2): 1587-0.

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Well Pai 2 is located at the Chepaizi high relief belt, west Junggar Basin. The Neogene Shawan Formation beach-sandbar in the Well Pai 2 is developed by lake wave reconstruction of fan-delta and reworking in its frontal side or flank, which was caused by lake transgression and fan oscillation on the basin slope, in the continuously dextral and uplifting of Chepaizi relief and under the compression background during evolution of the Tertiary quasi-foreland basin. Depositional and electric characteristics of the beach-sandbar are characterized by fine, loose grains, small thickness, two-stage cumulative probability curve, C-M chart showing PQRS paragraph mainly, moderate compositional and textural maturity, dactyline self-potential curve, and semi funnel-shaped resistivity curve. After light oil charging, the beach-sandbar reservoir show high amplitude, low-to-moderate frequency and high absorption coefficient, and its energy amplitude shows clear boundary, convex top and flat bottom. Beach-sandbar has prospects for good physical properties and lithologic reservoirs.

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Deposition confines hydraulic fracture length

ZHANG Lin; ZHAO Ximin; LIU Chiyang; ZHAO Yong; LI Zhihang and WANG Changling

, 2008, 35(2): 1588-0.

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The designing of hydraulic fracture length is traditionally based on reservoirs' physical properties and deliverability: producing formations of low permeability demand long fractures, while those of high permeability demand short fractures. However, the controlling function of deposition on hydraulic fracture length should also be considered in fluvial sedimentary formations. This paper gives evidence that river sandstone width confines fracture length using such methods as microseism, production analysis, pressure recovery, net pressure fitting. The Shihezi Formation in the Daniudi gas field is fluvial facies and hydraulic fracture surfaces orthogonalize the river orientation. Based on fracture spreading mechanisms and sandbody width, it is suggested that half fracture lengths in He 3 member be 90-120 m, and those in He 2 and He 1 members be 150-200 m.

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Geomodeling technology under multifactor control

REN Dianxing; LI Fanhua and LI Baozhu

, 2008, 35(2): 1589-0.

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Geomodeling technology under multifactor control is one kind of data processing for certain attributes modeling, which considers both the attribute data interaction and the other related data influences. So-called multifactor control includes three meanings: the attribute space formed by restrictions from other attributes; attribute deriving from other related attributes; attribute model adjustment by more reasonable models of other attributes. The key points of the modeling technology are processing of all kinds of faults, analysis and processing of complicated boundaries, structure calculation of certain small len formations controlled by structures of typical and large layers nearby etc. Model cases from different types of reservoirs in China indicate that it's easy and efficient for geologists to build delicate and reliable geological attribute models using the technology and by integrating all kinds of data related to the attribute models from static information to performance data into the original data or restriction data for geological modeling.

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Pore structure features of reservoirs at late high water-cut stage, Lamadian Oilfield， Daqing

LIN Yubao; ZHANG Jiang; LIUXiangui and ZHOU Hongtao

, 2008, 35(2): 1590-0.

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Lamadian Oilfield has entered a high water cut stage after long-term water-flooding, and injected water circulates in high permeability channels. Constant-rate and constant-pressure mercury injections were used to study the change of reservoir physical properties during development by water-flooding and the features of the reservoir pore structure before and after long term water flush. The constant-rate mercury injection analysis shows that the throat radii of main infiltration paths are enlarged and the pore radius distribution remains after long-term water-flooding, suggesting the infiltrating features are controlled mainly by throats instead of pores. The constant-pressure mercury injection analysis shows that water-flooding enlarges the pore throat radius median and maximum radius, increases large thorats and the corresponding pore throat distribution frequency and permeability. Both methods reveal that pore throats are enlarged after long-term water-flooding and large pore throats are the main path of fluid infiltration.

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A successful test with subdivision of oil layers and adjustment of water flooding in Gaotaizi oil zone, Daqing Oilfield

YAO Bo and ZHAO Qingdong

, 2008, 35(2): 1591-0.

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Gaotaizi oil zone has gone into a high water cut development stage, injecting water easily fingers through high permeability layers, and the conventional adjustments to water injecting projects are no longer efficient. To slow down the ascending rate of water cut, control the production decline and recover the residual oil to the utmost, it is necessary to subdivide oil layers and adjust water flooding. Subdivision is affected by the sublayer number and sandstone thickness in one segment, the variation coefficient between layers, the fingering coefficient in a single layer, and the thickness of interbeds between layers. Since the method is applied, injection profiles between and in the layers have been effectively improved, and the producing degree of the oil zones between connective oil wells increased. The oil output increased 18 t/d, the composite water cut decreased by 0.42%, and the formation pressure decreased 0.46 MPa.

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Method for improving history matching precision of reservoir numerical simulation

ZHU Yan; XIE Jin-zhuang; YANG Wei-hua and HOU Lian-hua

, 2008, 35(2): 1592-0.

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During reservoir numerical simulation, Darcy's law is usually used for splitting the flow based on formation capacity, without considering the effects of threshold pressure gradient of low-permeability. So the flow rate of the split layer is not consistent with the actual production, which results in poor history matching precision. Injection and production profiles are best information for determining the flow rate of individual layers. The matching is improved by flow split utilizing injection and production logs. To those wells without production logging, the flow split model is to be adopted according to the relationship of start pressure gradient and permeability. The application in the Unit 10-11 of Daqing Oilfield indicates that the history matching precision of reservoir numerical simulation was obviously improved, the coincidence rate of composite water cut of the whole area and that of single wells were increased by about 7% and 10% respectively.

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Laboratory study of ideal packing approach applying to high permeability sandstones

WAGN Jianhua; YAN Jienian; ZHENG Man and FENG Jie

, 2008, 35(2): 1593-0.

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It is difficult for conventional temporary bridging methods to seal large pore throats which usually make the dominant contribution to permeability. The reason is that the particle size of conventional bridging agents is optimized depending on the median pore size of target formation. High-permeability sandstone reservoirs have such features as wide permeability distribution range, great porosity, argillaceous cement, and wide distribution range of pore throat sizes. The key factors of reservoir damage are invaded particles and filtrate of drilling fluids, as well as the hydrate expansion and dispersion of clay. The KPAM polymer drilling fluids are optimized, ideal packing approach is applied to the drilling fluids, and the instrument of dynamic fluid loss test is used to evaluate return permeability. The test results indicate that the ideal packing approach can reduce the dynamic fluid-loss, improve the return permeability, and reduce breakthrough pressure.

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Application of material balance method to nitrogen anti-water-coning technology

PANG Zhanxi; CHENG Linsong; XU Jiafeng and FENG Ruyong

, 2008, 35(2): 1594-0.

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Nitrogen anti-water-coning is simplified into two processes of gas driving oil and oil driving water based on the mechanisms of nitrogen repressing water coning and enhancing oil recovery. Material balance method is employed to study nitrogen anti-water-coning technology in heavy oil reservoirs with bottom water and multi-periodic steam huff and puff. The calculation methods of gas-oil contact, water-oil contact, the oil volume enabled by injected nitrogen and the formation volume of enriched oil zone are established. The methods are applied to a production well of heavy oil reservoir with bottom water in the Shengli Oilfield， showing that injecting nitrogen for 20 days, 13 days and 10 days can push water coning to the original water-oil contact at nitrogen injection rates of 600, 900 and 1 200 m3/h (standard conditions), respectively. The technology can effectively control water coning and increase oil production during effective periods.

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Mechanisms and tests for hydraulic pulsed cavitating jet assisted drilling

LI Gensheng; SHI Huaizhong; SHEN Zhonghou; HUANG Zhongwei; LIAO Hualin and NIU Jilei

, 2008, 35(2): 1595-0.

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Based on modulating pulse jet and cavitating jet, a new drilling tool is designed which couples the advantages of both pulse jet and cavitating jet. When drilling fluid flows through the tool in drilling process, the fluid is modulated to pulse and cavitate. Thus, pulse cavitating jet is formed at the outlet of the bit nozzle. Because of jet pulsation, cavitating erosion and local negative pressure effect, bottomhole rock cleaning and breaking are enhanced and penetration speed improved. The tests in six wells show good applicability of the tool to bit types, formation, drilling fluid densities, flow rates and dynamic hydraulic drilling motors, etc. As the result, penetration speeds are improved by 10.1 to 53.4 percent and the maximum working time is about 235.5 hours in down-hole. Pulse and cavitating jet coupling will afford an effective means to improve drilling rate for deep wells.

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Oil resource of East Seram Island, Indonesia

YANG Xiaolan and LIU Xiaoping

, 2008, 35(2): 1596-0.

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Shows of abundant oil and gas including Bula oilfield and Oseil oilfield have been found in east Seram Island. The oil densities of wells BT-1, EN-1 and BPM-26 are 0.9-0.95 g/cm3, and their sulfur contents are 1.41% -2.69%. Analyses of group composition, carbon isotopic composition and biomarkers of crude oils reveal that the oils came from similar source marine carbonates. The Tertiary-Jurassic Saman-Saman marine marlite is the most likely source rock. Kobisonlah area and Dawang Masiwang area are two biggest oil generating centers. Oil maturity shows that two stages of oil generation and migration happened in this area. The generated oil migrated along thrusts and unconformities. Different thrust blocks had different oil sources. The discovered Oseil low maturity oil came from shallow Saman-Saman carbonates, while the Bula high maturity oil came from deeper Saman-Saman carbonates. The oil resource condition of the Seram Island is favorable.

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Queries about biogenesis of Quaternary gas in Qaidam Basin， NW China

MA Long; CHEN Hongde; ZHANG Jinglian; SHI Lanting and WEI Pingsheng

, 2008, 35(2): 1597-0.

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Organic geochemistry of Quaternary source rocks is not favorable to the generation of natural gas, such as the low organic matter content, the thin layer and the low ethanoic acid content in mudstones. Seven cases of natural gas occurrences show that the gas genesis can not be recognized by the current carbon isotope compositions. Five simulation experiments show that carbon isotopic fractionation can also happen in the Fischer-Tropsch reaction. Carbon isotope is not a reliable criterion for distinguishing biogenic from abiogenic gases. Based on 2 geo-transects and electromagnetic soundings, there is an uplifting upper mantle and 3 ultra-deep faults in the deeper crust, and there is a low velocity - high conductive layer in the mid-crust which is rich in CO2 (CO) and H2. If metal catalytic elements participated, the Fischer-Tropsch reaction might happen and formed hydrocarbons under certain temperatures and pressures. The deep crust structure shows that abiogenic gas might exist under the Quaternary System in the Qaidam Basin.

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, Volume 35 Issue 2