Petroleum Exploration and Development

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Tight gas in China and its significance in exploration and exploitation

Dai Jinxing; Ni Yunyan and Wu Xiaoqi

, 2012, 39(3): 2033-0.

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Tight gas reservoirs refer to the tight sandstone fields or traps accumulating natural gas of commercial values. According to reservoir characteristics, reserves, and structural height, they can be divided into two types, continuous-type and trap-type: the former are located at the lower part of the structure and have indistinct trap boundaries, inconsistent gas-water boundaries and reversal of gas and water, and their reservoirs are the same as or near the source; the latter are located at the higher part of the structure, with gas above water in traps, low reserves, and relatively high production. Tight gas in China is all coal-derived, dominantly alkane gases (C1—4), in which the amount of methane is greatest and the alkane gases have positive carbon isotopic series. The content of non-hydrocarbon gases (mainly CO2 and N2) is low. At the end of 2010, the reserves and annual production of tight gas in China accounted for 39.2% and 24.6% of the total natural gas, respectively, and the proportions are expected to increase. Compared to the shale gas and coalbed gas, tight gas should be considered in priority in the exploration and exploitation of unconventional gas in China.

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The hydrocarbon distribution characteristics under the control of basin type, structural unit and thrust belts in the foreland basins, central and western China

Song Yan; Zhao Meng Jun; Fang Shihu; Xie Huiwen; Liu Shaobo and Zhuo Qingong

, 2012, 39(3): 2034-0.

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Dominant factors controlling hydrocarbon distribution are analyzed from three aspects: the types, structural units and structural belts of the foreland basins of central and western China. There developed four types of foreland basins in China, superimposed, reformed, presenile, and new-generated foreland basins. Hydrocarbon distribution is different in the four types of basins and is controlled by their respective hydrocarbon accumulation conditions, characteristics and patterns. Thrust belts, fordeeps, slope belts and uplift belts are developed in foreland basins. The difference of these structural units in source rock development and evolution, trap type, hydrocarbon accumulation process, and preservation condition, cause different characteristics of hydrocarbon distribution in different structural belts. The main hydrocarbon enriched structural units are foreland thrust belts, in which the source rock and reservoir- caprock assemblage, structural configuration and the preservation conditions are the critical factors for hydrocarbon accumulation. The configuration of faults and cap rocks in thrust belts determines the features and enrichment regularity of hydrocarbon and indicates hydrocarbon enriched locations and favorable exploration targets in various structural belts.

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Guidance for seismic sedimentologic study in non-marine postrift basins

Hongliu Zeng; Xiaomin Zhu; Rukai Zhu and Qingshi Zhang

, 2012, 39(3): 2035-0.

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This study summarizes the research experiences of non-marine seismic sedimentology in recent years in China and uses Qijia area, Songliao Basin, as a template to establish general guidelines for seismic sedimentology. Basic data sets include stacked 3D seismic volumes, 2D regional seismic lines, data for regional geologic settings, and well data. The workflow emphasizes the integration of seismic and geologic interpretations and balanced use of seismic sedimentology, sequence stratigraphy and seismic stratigraphy. Basic steps include well-to-seismic tie for the establishment of sequence framework, wavelet-phase adjustment, picking of geologic-time parallel seismic events, seismic resolution analysis, petrophysical analysis, selection of seismic attributes, stratal slicing, seismic depositional facies analysis, and applications to exploration and development. Expected maps range from key interpreted well-seismic sections, flattened relative geologic-time sections, stratal slices, and depositional facies maps, etc. The workflow is applied in the study of the Cretaceous Qingshankou Formation in the Qijia area, Songliao Basin, which can be used as a reference for seismic sedimentologic study in non-marine basins, especially in postrift depression-type basins in China.

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Recognition and distribution of marine hydrocarbon source rocks in the Ordovician and Cambrian of the Tarim Basin

Zhang Shuichang; Gao Zhiyong; Li Jianjun; Zhang Baomin; Gu Qiaoyuan and Lu Yuhong

, 2012, 39(3): 2036-0.

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A process for identifying marine hydrocarbon source rocks is established based on outcrop measurement, ground-penetrating radar survey, core analysis, logging evaluation, seismic interpretation, etc. It is used to identify the Cambrian and Ordovician marine hydrocarbon source rocks and to predict their spatial distribution in the Tarim Basin. There developed four suites of marine hydrocarbon source rocks in the Tarim Basin, which are distributed, respectively, in the Lower-Middle Cambrian of the Awati and Manjiaer sags, the Heituao Formation of the Lower-Middle Ordovician in the Tadong region, the Saergan–Tumuxiuke–Queerqueke formations of the Middle–Upper Ordovician from the Awati Sag to the Manjiaer Sag, and the Yin’gan and Lianglitage formations of the Upper Ordovician from the Awati Sag to the Tazhong area. The development of these source rocks is controlled by the sea level rise and they are characterized by different facies in the same stage, namely, different source rocks are deposited in sedimentary facies zones at the same stage. The formation of the source rocks migrates with the carbonate basin and stops when there are large quantities of clastics poured in.

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Accumulation conditions and exploration and development of tight gas in the Upper Paleozoic of the Ordos Basin

Yang Hua; Fu Jinhua; Liu Xinshe and Meng Peilong

, 2012, 39(3): 2037-0.

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Through lithological analysis of reservoirs, fluid inclusion test and simulation experiment, combined with geochemical, seismic, well logging and formation testing data, this paper studies the favorable geological conditions for tight gas accumulation in the Upper Paleozoic of the Ordos Basin, specifies the characteristics of tight gas reservoirs, and summarizes the key techniques for tight gas exploration and development. The gas source conditions of large area hydrocarbon generation and continuous hydrocarbon injection, widespread delta facies sandstone reservoirs, and the accumulation mode of short-distance migration facilitate the formation of the large-scale tight gas reservoirs in the Upper Paleozoic of the Ordos Basin. The Upper Paleozoic tight gas reservoirs in the Ordos Basin cover a large area and have many gas-bearing formations and multiple pressure systems. The tight reservoirs, which were formed before gas accumulation, are of high heterogeneity. Full digital seismic prediction technique for thin reservoirs, fine logging evaluation technique for tight gas reservoirs, and integrated supporting techniques for gas development provide technical support for further exploration and development.

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Sequence structure and non-structural traps of the Paleogene in the Weixi’nan Sag, Beibuwan Basin

Wang Jian; Cao Yingchang and Li Junliang

, 2012, 39(3): 2038-0.

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Based on Vail sequence stratigraphic theory and analysis of seismic and logging information, the sequence in the Paleogene Liushagang and Weizhou formations in the Weixi’nan Sag is classified, the strata framework of sequence is defined and established, the characteristics of sequence structure are analyzed and the distribution of non-structural traps is revealed. One first-order sequence boundary, two second-order sequence boundaries, eight third-order sequence boundaries and ten third-order sequences are identified in the Liushagang and Weizhou formations. According to the characteristics of sequence boundary structure, the third-order sequence boundaries can be divided into three types: type T1, type T2, and type T3. And according to the characteristics of sequence stratigraphic structure, the ten third-order sequences can be classified into four types: one-divided sequence, two-divided sequence, three-divided sequence, and four-divided sequence. The favorable areas for the development of stratigraphic overlap traps are above type T1 and type T3 sequence boundaries, while the unconformity barrier traps are developed below type T2 and type T3 sequence boundaries. The favorable development periods of lithologic traps are the early period of three-divided sequence and four-divided sequence and the late period of two-divided sequence and four-divided sequence.

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Stable carbon isotopic compositions and its significance of water-soluble gases

Qin Shengfei

, 2012, 39(3): 2039-0.

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Twenty-two gas and twenty-two water samples were collected from producing wells in the Triassic Xujiahe Formation, Leikoupo Formation and Jialingjiang Formation and the Permian Maokou Formation, in the Middle Sichuan, South Sichuan and Northwest Sichuan gas areas. The difference of carbon isotopes was compared between free gas and water-soluble gas. The component and carbon isotopic composition of the free gas showed normal characteristics of organic gas, while the alkane gas released from gas field water had more 13C component, indicating that gas field water plays an obvious role of fractionation in carbon isotope of natural gas. During the gas accumulation, if much gas is released from formation water and mixed into free gas, the carbon isotopic composition of free gases may become heavier. So, the carbon isotopic composition of water-soluble gases provides a new perspective for the study of gas origin and gas accumulation mechanism. Mixing of gases released from formation water may be the factor causing the carbon isotope anomalies for natural gases from the Kuqa Depression, Tarim Basin; Jiulongshan region and Weiyuan gas field, Sichuan Basin; and volcanic gas reservoirs of the Songliao Basin.

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The Discussion of Tridimensional Development Mode of Reservoir

Ren Fangxiang

, 2012, 39(3): 2040-0.

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In order to realize the effective development of buried hill light oil reservoirs, mid-deep massive heavy oil reservoirs with interbeds, and ultra-deep massive heavy oil reservoirs in the Liaohe Oilfield, three tridimensional development models are established: superposition of horizontal wells in multi-intervals and multi-layers, steam assisted plane displacement (vertical wells) with combination of vertical gravity drainage (horizontal wells), and steam assisted liquor drainage by two superposed horizontal wells and production by vertical wells. The development mechanisms for these three tridimensional development models have been studied by field test, physical simulation and numerical simulation. The tridimensional development mechanisms of buried hill light oil reservoirs are uniform compaction action, vertical gravity action and joint supply action. The tridimensional development mechanisms of mid-deep massive heavy oil reservoir with interbeds are gravity drainage and steam flooding, and the tridimensional development mechanisms of ultra-deep massive heavy oil reservoir are gravity water drainage, reduction of heat losses and enhancement of production injection ratio. The field tests in the light oil reservoir of the Xinggu buried hill, mid-deep massive heavy oil reservoir in Xing Ⅵ oil layer of Block Du 84 and ultra-deep massive heavy oil reservoir of Block Wa 59 in the Liaohe Oilfield showed that tridimensional development can significantly improve crude oil production, and realize efficient development of oilfield.

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Schemes for automatic history matching of reservoir modeling: A case of Nelson oilfield in the UK

Kazemi Alireza and Stephen Karl D

, 2012, 39(3): 2041-0.

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Schemes for automatic history matching of reservoir modeling are studied for the Nelson oilfield in the Central North Sea. A complete workflow of automatic history matching involves selection of reservoir variables that require modification and parameter updating schemes, automatic history matching, data analysis, and combination of the best results to obtain an ensemble of best reservoir models. Automatic history matching of Nelson field is conducted using production and time-lapse seismic data, with global single-variable approach, regional multi-variable approach and local multi-variable approach as updating schemes, net to gross, horizontal and vertical permeability as updating parameters. Three parameter updating schemes, i.e. global single variable approach, regional multi-variable approach and local multi-variable approach, are introduced, in order to reduce the number of simulations significantly and make automatic history matching workable. They are applied for history matching of Nelson field using production and time-lapse seismic data. It is revealed that local multi-variable approach can effectively improve history matched results byis very useful for reducing the number of simulation models, saving computing time and increasing the simulation precision. Global single-variable approach is only a suitable parameter updating scheme for cases where the history matching parameters are independent. Regional multi-variable approach is suitable for the cases where there is strong dependency between properties chosen for updating, and there are wells very close together with strong interaction. Local multi-variable approach is very useful when the history matching parameters are dependent but each selected region for updating is independent of others.

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New understanding on water-oil displacement efficiency in a high water-cut stage

Ji Shuhong; Tian Changbing; Shi Chengfang; Ye Jigen; Zhang Zubo and Fu Xiujuan

, 2012, 39(3): 2042-0.

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Based on analyzing dominant internal and external factors affecting water-oil displacement efficiency, the variation of oil displacement efficiency is studied by means of experimental and theoretical analyses. Internal factors include reservoir heterogeneity (highlighted micro-pore structure heterogeneity) and wettability. External factors are waterflooding conditions, including pore volume multiplier of water injected, injection rate, and oil-water viscosity ratio. The variation mechanism is analyzed based on the definition, laboratory determination and field application of water displacement efficiency. A viewpoint is proposed that the changes of wettability and pore structure in a high water-cut stage would reduce the critical capillary number and the residual oil saturation, leading to improvement of water displacement efficiency. More attention should be paid to water-oil displacement efficiency when water-flooding oilfield enters a high water-cut stage. Research on water-oil displacement efficiency must be deepened from three levels as follows: the first is the definition of laboratory values, the second is to study economic and effective conditions for getting (reaching) a certain oil displacement efficiency, the third is how to develop cost-effective techniques to improve the displacement efficiency by increasing capillary number.

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The progress in the alkali-free surfactant-polymer combination flooding technique

Zhu Youyi; Zhang Yi; Niu Jialing; Liu Weidong and Hou Qingfeng

, 2012, 39(3): 2043-0.

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Alkali-free surfactant-polymer SP flooding can avoid scaling, strong emulsification and corrosion caused by alkali, thus reducing the investment and operating cost. It is a new chemical flooding technology for Enhanced Oil Recovery (EOR) with a promising application prospect. The main problems of SP flooding are as follows: shortage of industrialized surfactant product of high performance, weak theoretical research on oil displacing mechanisms and main influencing factors, unsound evaluation methods, lack of pilot tests, and high technical risk. The main factors that affect the oil displacement efficiency of SP flooding are displacing fluid viscosity, interfacial tension, and emulsification strength of SP system. The high viscosity of SP flooding formula system is an important guarantee of EOR process. The lower the interfacial tension, the higher the oil recovery degree. The emulsifiability of SP system can significantly affect efficiency of oil displacing. SP flooding process has obtained certain effects in pilot tests but there are still some problems. The formula adaptability and quality stability of surfactant product should be improved, the injection program should be optimized, and the field monitoring and process tracking and regulation should be strengthened.

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Volume Fracturing Technology of Unconventional Reservoirs —— Connotation, Optimization Design and Implementation

Wu Qi; Xu Yun; Wang Xiaoquan; Wang Tengfei and Zhang Shouliang

, 2012, 39(3): 2045-0.

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The connotation, optimization design and implementation of the volume Fracturing technique are discussed. The connotation includes five aspects as follows: (1) break up reservoirs to form complex fracture network, and “create” the artificial permeability; (2) fracture initiation is not single open-fracture but shear failure and slip; (3) “breakthrough” the traditional fracturing seepage theory model, greatly shorten the effective fluid seepage distance; (4) more suitable for high brittleness formations; (5) multi-stage and multi-cluster perforation mode. Research shows that: the time required to seep through matrix (0.000 001 ′ 10-3 μm2) to fracture for 100 m distance is about more than 100 × 104 years, and only volume fracturing can realize “the most short-distance” seepage. Cluster spacing optimization, non-uniform stage (cluster) interval and proppant transportation are the key to achieve volume fracturing. Small cluster interval technology, multiple stop-injection mode and tip screen-out fracturing technology are the key techniques to realize volume fracturing in low brittleness formations. Volume fracturing technique has a good application prospect in tight oil (gas), volcanic and carbonate, and the further developed “integrated” volume fracturing (based on multi-layer and multi-branch well technology) is the future development direction of unconventional reservoir development.

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The novel fluid loss additive HTF-200C for oil field cementing

Guo Jintang; Lu Haichuan; Liu Shuoqiong; Jin Jianzhou and Yu Yongjin

, 2012, 39(3): 2046-0.

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The domestic fluid loss additives often have lower thermal stability and poor salt-tolerance and their comprehensive properties are not good enough. To solve the problems, a novel cement fluid loss additive HTF-200C, which can resist high temperature and high salt content, was synthesized using the monomers of 2-acrylamido-2-methyl-propane sulphonic acid (AMPS), N, N-dimethyl acrylamide (DMAA) and a new compound with double carboxyl by the method of aqueous solution polymerization. The microstructural characterization and application performance of HTF-200C show that the polymer with the structure of all the monomers has an excellent thermal stability and strong salt tolerance, and can be used in 200 ℃ or in saturated brine. And the problem of the normal fluid loss additive being easy to hydrolyze due to high temperature can be solved with HTF-200C. What’s more, it can also deal with the bulge of thickening curve in consistency test. The cement slurry prepared mainly by HTF-200C presents good comprehensive properties such as low filtration, high thermal stability, strong salt tolerance, rapid development of strength in low temperature, without far delayed solidification, short transit time during thickening process, and so on. The cementing job quality of Well Chengu 1-3 in the Liaohe Oilfield is excellent after it is used.

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Seismic oil reservoir description key technologies of high water-cut oilfields

Gan Lideng; Dai Xiaofeng; Zhang Xin; Li Linggao; Du Wenhui; Liu Xiaohong; Gao Yinbo; Lu Minghui; Ma Shufang and Huang Zheyuan

, 2012, 39(3): 2047-0.

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Reservoir characterization in mature oil fields with high water cut faces the challenges of small geological bodies, large well density, and data acquisition spreading over long periods. To solve these problems, systematic research on seismic reservoir characterization was carried out, and a technical solution was proposed based on well-controlled seismic data processing, well-controlled seismic data interpretation and well constrained seismic inversion. This technical route includes five suites of key technologies. (1) Rock physics analysis, including seismic reservoir-prediction-oriented well log processing and interpretation, rock physics modeling and its application, selection of parameters sensitive to lithology, physical property and hydrocarbon. (2) Well-controlled seismic data processing, including well-controlled high-resolution data processing, amplitude-preserved data processing and quality control. (3) Well-controlled fine structure interpretation, including well-controlled minor fault interpretation, well-controlled seismic horizon tracing and well-controlled structure mapping. (4) Well-constrained seismic inversion, including deterministic inversion and stochastic inversion. (5) Seismic-constrained reservoir modeling and numerical simulation. Although well density is large in a high water cut oil field, reservoirs between wells cannot be clearly defined by known well data. The effect of seismic reservoir characterization can be improved significantly only by bringing dense well data into full play and by combination of multi-disciplinary.

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Dynamic effect of capillary pressure in low permeability reservoirs

Tian Shubao; Lei Gang; He Shunli and Yang Limin

, 2012, 39(3): 2048-0.

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The dynamic effect of capillary pressure in oil-water two-phase percolation flow in low permeability reservoirs was investigated by experiment and numerical simulation. An experimental apparatus was constructed to measure the relationship between the dynamic capillary pressure and water saturation change rate, and the dynamic capillary coefficient of low-permeability cores was calculated. A one-dimensional mathematical percolation model was established to analyze the effect of dynamic capillary pressure on waterflooding process. The dynamic capillary pressure effect is too significant to be neglected. The relationship between the dynamic capillary pressure and the change rate of wetting phase saturation is almost linear. The lower the rock permeability is, the greater the dynamic capillary coefficient and threshold pressure gradient are. One of the reasons for non-Darcy two-phase percolation flow is the dynamic capillary pressure effect. The dynamic capillary pressure in low permeability reservoirs has a significant influence on development indices such as the velocity of displacement front, water breakthrough time, pressure distribution, oil production rate, and recovery degree.

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, Volume 39 Issue 3