Publisher(s): China Academic Journals (CD Edition) Electronic Publishing House Co., Ltd.
ISBN: ISBN 978-7-499-00964-6 pdf
First Published: 2020.11.23
Discipline(s): Chemistry/ Metallurgy/ Environment/ Mine Industry
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Shale oil and Shale Gas, as part of China’s S&T Progress Series, has 35 representative excellent articles on shale oil/gas research in China. It focuses on the integration of basic theories and methods related to shale oil/gas. The chapters cover reservoir geological evaluation, dynamic development progress, drilling technology application, and other core research aspects on shale gas reservoir. The book can be used as a reference for senior managers of petroleum enterprises, experts and scholars of oil/gas research institutions and colleges/universities, and library readers worldwide.
Doctor Lu Baoping has initiated the description theory of drilling geological environmental factors, introduced the methods for optimizing drilling technology based on this theory, created a complete technology chain unique to China for shale gas engineer
Petroleum Geology and Recovery Efficiency,Part 1: Progress in Shale Oil Exploration and Development,Vol 26,No. 01
By reviewing the exploration process of the Paleogene–Neogene shale oil in Jiyang Depression, the theoretical achievements and the technology series obtained from the previous shale oil exploration were summarized and the elements of shale oil enrichment of the Tertiary in Jiyang Depression were analyzed. Besides, the direction of shale oil deployment was pointed out considering the actual situation of drilled shale oil wells. Exploration practice shows that the continental shale oil in Jiyang Depression is different from the marine shale oil that has been drilled successfully in North America, which is characterized by strong heterogeneity, weak diagenesis, and low maturity. Theoretical innovation and new exploration ideas are necessary to establish the relevant supporting technologies and methods suitable for eastern continental shale oil exploration as soon as possible. The complexity of the occurrence pattern of continental shale oil requires a classified step-by-step exploration. The mixed shale oil in the interlayer, micro-crack and high-quality lithofacies should be first developed. On the basis of its effective economic production, the implementation of the matrix shale oil drilling and deployment will be carried out next, and the target optimization evaluation system suitable for eastern continental shale oil should be improved as soon as possible, in order to open up new exploration targets to increase the reserve of old oilfields.
Petroleum Geology and Recovery Efficiency,Part 1: Progress in Shale Oil Exploration and Development,Vol 26,No. 02
Shale oil is an important component of unconventional hydrocarbon. It mainly exists in different types of pores and fractures of shale. Unlike the shale at high maturity stage which generates shale gas, the hydrocarbon pore space in organic shale at the oil-generating window is often filled completely or partially by early hydrocarbon-generating materials, thus affecting the structure characterization and geometry description of shale oil pore spaces. Through the microscopic observation of a large number of shale samples, the pores of shale oil reservoirs could be divided totally into intergranular mineral pores, intragranular mineral pores and organic pores. The former two types of pores include intergranular pores among different mineral particles, dissolution pores, and clay mineral interlaminar pores. The organic pores are composed by marginal shrinkage pores (fractures) and a small amount of pyrolysis pores. Based on the requirement for characterization of shale oil pores, solvent extraction is carried out on the samples, and the suitable pore characterization techniques for crushed and blocked samples are discussed respectively. Different shale oil characterization methods have certain differences in principles and application and have certain limitations as well. In order to avoid the influence of this factor on pore characterization, a variety of characterization methods can be combined to characterize pores through comparative analysis and unified dimension, so a to improve the accuracy of pore characterization results of shale oil reservoirs.
3. Petroleum geological characteristics and hydrocarbon discovery of shale system in fine-grained sedimentary area of lacustrine basin: A case study of Kong2 Member in Cangdong Sag, Huanghua Depression
Petroleum Geology and Recovery Efficiency,Part 1: Progress in Shale Oil Exploration and Development,Vol 26,No. 03
According to the traditional view, the semi-deep–deep lake area in the lacustrine basin is mainly dominated by the relatively homogeneous mudstone shale with high clay and low terrigenous clast, which is a forbidden area for hydrocarbon exploration. But in recent years, the exploration and discovery of shale oil and gas in China and abroad has completely broken through the traditional understanding. In order to research the basic geological characteristics of shale systems in the fine-grained sedimentary area of the lacustrine basin, based on 635 m cores of wells G108-8, GD14 and GD12, more than 8 000 analytical laboratory data and matching logging data, the lithologic characteristics, reservoir characteristics, organic geochemical characteristics and their influence on the reservoir transformation of Kong2 Member in Cangdong Sag, Huanghua Depression were studied. It is found that the mineral composition of the shale system in Kong2 Member is complex and the rock types are diverse. According to the X-ray diffraction (XRD) mineral composition, the shale system can be divided into three categories and seven sub-categories, such as felsic shale, limy dolomite and hybrid shale. The shale system not only has the ability to generate oil but also has a certain storage capacity, in which there are many kinds of pores and fractures, such as organic pore, intergranular pore, and micro-fracture. The shale can be easily stimulated as well. The abundance of organic matters and the maturity of thermal evolution have obvious effects on the porosity development, oil content and carbonate crystallization of shale oil reservoirs. The differences in mineral composition and structure of shale result in differences in petroleum geology among different rocks. Hydrocarbon of short-distance migration should look for in limy dolomite, while the hydrocarbons of in-situ retention should mainly look for in felsic shale and hybrid shale. All the three types of shale are beneficial for shale oil storage, but different types of shale should be stimulated by different engineering measures to maximize the exploration and development of shale oil.
4. Molecular Geochemical Evaluation of Shale Oil Mobility–A Case Study of Shale Oil in Jiyang Depression
Petroleum Geology & Experiment,Part 1: Progress in Shale Oil Exploration and Development,Vol 40,No. 04
Shale hydrocarbon potential, shale oil mobility and shale compressibility are three important factors of geological evaluation for shale oil exploration and development. Among them, the shale oil mobility is constrained by the pressure system, shale hydrocarbon potential, shale oil composition and occurrence space. Since there were no standardized methods or criteria for shale oil movability evaluation, a combination of multiple parameters (pyrolysis parameter S 1, S 1/ w(TOC) and pore-throat median radius) together with exploration and development practice have been used for comprehensive characterization. Based on the experimental analysis of a large number of core samples for shale oil exploration in the Jiyang Depression, a coupling relationship among shale oil molecular composition, shale hydrocarbon potential and shale oil occurrence space was found, and a molecular geochemical evaluation model for shale oil mobility was established. The study revealed that when the ratio of ∑ nC 20?/∑ nC 21+ was < 1, pore-throat median radius is generally > 20 nm. Under this condition, pyrolysis S 1 was usually > 3 mg/g and S 1/ w(TOC) was > 100 mg/g. The ratio of ∑ nC 20?/∑ nC 21+ basically remained constant with the increase in S 1, the ratio S 1/ w(TOC) and shale pore-throat median radius. This indicated that when shale pore-throat radius reaches a certain level, hydrocarbon molecular diffusion is not affected by diffusion energy barriers, and shale oil molecule occurrence in pore throats is relatively homogeneous, so shale oil has good fluid mobility. When the ratio of ∑ nC 20?/∑ nC 21+ was > 1, shale pore-throat median radius was usually < 20 nm. At this time, pyrolysis S 1 was commonly < 3 mg/g, and S 1/ w(TOC) was < 100 mg/g. The ratio of ∑ nC 20?/∑ nC 21+ was increasing quickly with the decrease in S 1/ w(TOC) and shale pore-throat median radius. It indicated that when the shale pore-throat median radius becomes small, diffusion energy barriers limited the diffusion of macromolecular hydrocarbon components in pore throats, and thus shale oil has poor fluid mobility, and low molecular weight hydrocarbon is the main constituent to flow easily. In such a condition, shale has poor content of free oil. The lowest limit of pore-throat radius for shale oil flow in the Jiyang Depression is approximately 20 nm.
5. The Effect of Threshold Pressure Gradient and Stress Sensitivity on Shale Oil Reservoir Productivity
Petroleum Drilling Techniques,Part 1: Progress in Shale Oil Exploration and Development,Vol 45,No. 05
In order to research on the effect of threshold pressure gradient and stress sensitivity on the productivity of shale oil well, a mathematical model that took into consideration of the threshold pressure gradient and stress sensitivity for shale oil seepage was developed on the basis of oil–gas–water three-phase seepage model. A numerical solution method was offered and numerical simulator of shale oil reservoir was compiled. Patterns and mathematical rules for threshold pressure gradient and stress sensitivity on horizontal well productivity of multi-stage fracturing shale oil reservoir were analyzed by using a numerical simulator of shale oil reservoir. The calculation results on the degradation of the simulator were basically identical with Eclipse software calculation results, which validated the correctness of the simulator. The numerical simulation results showed that the cumulative oil production rate for 10 000 days was 24.7% of that where there was no threshold pressure gradient when the threshold pressure gradient reached 0.5 MPa/m. When the stress sensitivity coefficient rose from 0.1 MPa ?1 to 0.5 MPa ?1, the reservoir permeability near borehole zones dropped approximately one order of magnitude and the cumulative oil production rate was 36.2% that of no stress sensitivity effect after 10 000 days’ production. Moreover, the cumulative oil production was lower while simultaneously considering the threshold pressure gradient and stress sensitivity effect. The results showed that the threshold pressure gradient and stress sensitivity effect both greatly inhibited shale oil productivity and the shale oil productivity might be overestimated without consideration of the threshold pressure gradient and stress sensitivity effect. Therefore, a numerical simulator of shale oil reservoir can provide the guidance for development of shale oil reservoirs.
Progress in Geophysics,Part 1: Progress in Shale Oil Exploration and Development,Vol 33,No. 06
In order to evaluate the fracability of shale oil reservoirs, we took the Chang 7 shale oil reservoirs in the Ordos Basin as an example, calculated the brittleness index and fracture toughness index by using the existing well logging data of the fractured wells in the study area, drew the fractured profile, and combined with the brittleness index and fracture toughness index to establish a new evaluation model, which can provide preliminary guidance for choosing positions and wells in the fracturing process, and basis for the screening of shale oil favorable area and the forecast of production capacity after fracture. The model was applied to L70 well, L58 well and L295 well in the study area. The fracture distribution and fracturing effect of each well were evaluated by combining with the fractured profiles and anisotropic production diagrams of pre-frac and post-frac, and the results were compared with the actual fracturing effect of each well. The evaluation results showed that the brittleness was one of the important factors of the shale oil reservoirs fracturing, but some reservoirs with strong brittleness may not be highly fractured. Combining with the brittleness index and fracture toughness index can evaluate shale oil reservoirs fracability more accurately and effectively. Compared with the adjacent sandstone section, the Chang 7 shale oil reservoir had a lower level of natural fracture development, higher crustal stress and lower brittleness. It is suggested that the favorable areas should be chosen at the shale oil reservoirs with lower crustal stress, stronger brittleness, smaller fracture toughness and lager fracability coefficient.
7. Breakthrough of risk exploration for Class II shale oil in Chang 7 member of Yanchang Formation and its significance in Ordos Basin
China Petroleum Exploration,Part 1: Progress in Shale Oil Exploration and Development,Vol 25,No. 07
In 2019, the Changqing Oilfield Company deployed two horizontal wells to carry out the risk exploration test for shale oil (Class II shale oil) of thick shale interlayered with thin layers of siltstone and fine-sandstone in the 7 3 (Chang 7 3 member) member of Yanchang Formation in the Ordos Basin. Oil flows with high production of 121.38 t/d and 108.38 t/d have been obtained in the two horizontal wells, Well Chengye–1 and Well Chengye–2, which significantly promotes the exploration progress of Class II shale oil. In this paper, the cores, thin sections, well loggings, and geochemical data of two horizontal wells and the pilot well of Well Chengye-1 were mainly used to study the reservoir conditions and resource potential of Class II shale oil reservoirs in Chang 7 3 member. The results show that the reservoir type penetrated by horizontal sections of the two horizontal wells was mainly the thick shale interlayered with several thin siltstone and fine-sandstone layers. The perpendicular thickness of the sand body of single layer was 1–5 m. The lateral extension length of the sand body along the horizontal direction was mainly distributed in 25–50 m. The lateral wide of the sand body was 100–300 m. The distribution area of the single sand body was small. The reservoir types included intergranular pores, dissolution pores, intragranular pores, inter-crystalline pores, organic pores, and fractures. The radius of intergranular pores was concentrated in 0.1–3 μm, which is up to 21 μm. In the reservoirs penetrated by pilot section and horizontal sections, the high-conductive fractures and other fractures were well developed and distributed in E-W direction. The porosity of the sandstone reservoirs was 6%–12%, and the permeability was generally less than 0.3 mD. Shale reservoirs were of poor reservoir performance with porosity less than 2% and permeability less than 0.01 mD. By using methods such as rock pyrolysis, petroleum ether extraction, and dichloromethane extraction, we evaluated the movable shale oil resources in shale and sandstone in Chang 7 3 member within the area of 220 km 2 in Cheng-80 block. The preliminary evaluation results were (0.692–0.783) × 10 8 t. The distribution area of Class II shale oil in Chang 7 3 member in the Ordos Basin was about 1.5 × 10 4 km 2, and the prospective resources of Class II shale oil in Chang 7 3 member were 33 × 10 8 t.