Recently, shale gas research and industrial production in China have been greatly developed, which has enriched the theory of natural gas geology in China and increased the supply of domestic natural gas production. In the future, shale gas will obtain great achievements among the developments of natural gas industry in China. The following four geological and geochemical issues about the exploration and research of shale gas has great
(1) China has to break through the single economic shale gas formation. The United States found at least 30 sets of economic shale gas formations in 29 basins. To date, only one basin in China (Sichuan Basin) has found one set of economic shale gas formation (Wufeng-Longmaxi formations). (2) Interval RO value of the economic shale gas formations and segment RO value of the gas fields. The interval RO values are 3.31% for the economic shale gas formation in China and 4.1% for that in USA; the segment RO values are 2.34% for the gas fields in China and 3.5% for that in USA. The former values are small and the latter values are big. A number of shale gas fields derived from sapropelic sources in the United States were found in the oil generation window with RO of 1.0%-1.3%. So shale gas exploration in China also needs to pay attention to this stage. At the same time, attentions should be paid to the exploration of shale gas derived from humic sources. (3) The continuous high-yield period of gas field. The world's first commercially developed shale gas field (Barnett) shows a high-yield forecast of 100×108 m3 per year of about 20 years.Development of shale gas field in China is still in the construction stage. (4) The role of fracture in shale gas preservation and development. The fault has dual effect on the enrichment of shale gas. In the United States, tectonic in the shale gas basin is stable and faults are few, while in China structures in the shale gas basin are active and faults are developed. Therefore, faults have more harm than good to the shale gas in China, which caused the fragmentation of the continuously distributed Wufeng-Longmaxi formations, limiting the area of gas field.
Songliao Basin is a large-scale petroliferous basin with a dual-texture of depression in Mesozoic. There are numerous sags developed in the fault depression and the exploration degree aimed at those sags is low, which makes it a strategic replacement fields in the future exploration. In the big deep fault depressions such as Xujiaweizi Sag, Changling Sag, great breakthroughs in natural gas exploration have achieved and large-scale reserves have been discovered. However, oil and gas exploration has not made a big breakthrough in other Sags. Recently, the breakthrough of oil exploration in Shuangcheng Sag further confirmed the exploration potential in the depression. Previous studies have shown that the hydrocarbon accumulation and distribution in the fault depression of Songliao Basin are controlled by sag structures. According to the structural characteristics of different areas in Shuangcheng Sag, the structure of it can be divided into six models including central fault horst type, central fault graben type, single fault trough type, double fault trough type, multistage fault type and half fault graben type, and seven accumulation models were accordingly constructed. It is pointed out that the four major complex hydrocarbon accumulation zones including central fault buried hill structural belt, buried hill structural belt of slope fault, buried hill structural belt of steep slope fault and strike-slip anticlinal belt will be the favorable exploration areas in Shuangcheng Sag in the future. The faulted anticline, fault block, fault-nose and buried hill traps are the next exploration targets. For those favorable structural belts, multi-layers and multi-objective types of stereoscopic exploration ideas should be applied, and we should give priority to the central fault buried hill structural belt should be given priority in order to achieve discovery. Then, we can extend the exploration areas to slope fault buried hill structural belt and buried hill structural belt of steep slope fault to realize breakthroughs in new zones. And also we should explore the replacement field of lithologic stratum reservoirs in order to implement the benign development in the exploration of this field.
The content of gypsum salt rock in Cambrian drilling in Sichuan Basin is counted. The distribution of gypsum salt rock is characterized by combining logging and seismic data. The Cambrian developed area of Sichuan Basin is divided into the undeveloped area of gypsum salt rock mainly in the ancient uplift and slope area of Leshan-Longnusi and the developing area of gypsum salt rock mainly in the area of Chuandong-Shunan. The observation and description of core and thin-section reveal that the main types of reservoir rocks are dolograinstone and dolopackstone. The reservoir space includes three categories and nine subcategories: pore type, cave type and fracture type, and the cavern type is the main type. Physical properties test show that the porosity of core is below 2% and the reservoir is above 3% in non-gypsum developed area. The core porosity is 3.5% on average and up to 5% in the development area of gypsum salt rock. Microfacies are the basis of reservoir development in the Xixiangchi Formation, and grainstone beach is the main microfacies type. The atmospheric fresh water karst is the main controlling factor for the formation of high quality reservoir in undeveloped area of gypsum salt rock. The superimposition of burial dissolution is the key to the formation of high quality reservoir in developed area of gypsum salt rock. The potential of oil and gas exploration in Xixiangchi Formation is prospected. The paleo uplift and slope area of undeveloped gypsum salt rock should be based on searching for high-quality beach reservoir influenced by the karst of atmospheric fresh water. It is an important field of exploration breakthrough to find buried dissolved and superimposed reservoir in the east-shunan area of Cambrian gypsum salt rock.
Based on data from cores, rock slices, scanning electron microscope, granularity, X-ray diffraction, porosity and permeability, and X-ray fluorescence, this paper makes a comparative analysis of lithology, sedimentary textures, mineral composition, major elements and permeability, and then proves that the cores of Lulehe Formation from Wells of Maxi 5, Maxi 6, Xiandong 1 and Xiandong 2 in Maxian area belongs to aeolian sandstones, existence of which is the first time to be revealed in the Lulehe Formation of the Qaidam Basin. These aeolian sandstones are brown yellow medium-fine sandstones with loose cementation. Compared with the water-laid sedimentation, the aeolian sandstones have the characteristics of single lithology, thick sand layer, high compositional maturity, good roundness of quartz particles with surface textures of aeolian sand, and the particle size similar to modern aeolian sand. The aeolian sandstone is obviously distinguished from water-laid sedimentation in Zircon-kK-feldspar-plagioclase, A-CN-K ternary diagram, PCA analysis and MFW ternary diagram. In addition, according to the analysis of sedimentation and provenance, it is considered that aeolian sandstones are deposited in the transitional zone of the alluvial fan and alluvial plain, the sediments of which experience the process of re-transportation, sorting and re-deposition of wind. The sedimentary model can be widely applied to support the sedimentary and reservoir research during the process of petroleum exploration and development in the northern margin of Qaidam Basin.
In this paper, through detailed observation and fine measurement of outcrop profile in Quanji area of Qaidam Basin, the stratigraphic characteristics, sedimentary facies types and evolution rules are analyzed in detail. The results show that there is evidence for shallow lake sedimentation in the Qigequan Formation in the study area. Grain size of the rock from the lower part of the Qigequan Formation is fine, and gradually coarse to the upper part. There are mainly three types of sedimentary facies: Lake, beach bar and fan delta, which are in the whole process of retrograde sedimentation. The lake is mainly composed of lakeside and shallow lake argillaceous siltstone, with gravel bearing coarse sandstone and medium coarse sandstone with rich plastic deformation structure, belonging to the storm sediment products. The beach bar is further divided into distal bar sand, nearshore bar sand and mudflat. The bar sand is shown as gray medium and thick sandstone with lenticular mudstone. The beach sand is mainly composed of medium thin layer of siltstone; the fan delta is mainly composed of thick layer of gray conglomerate and medium coarse sandstone. Based on the comparative analysis of the sedimentary facies of several dew points in the profile, the lateral change law of the sedimentary facies and the spatial distribution law of beach bar sand body are clarified, and the beach bar sand sedimentary model of the area is established for the first time.
Multi-point geostatistics is widely used in the establishment of geological models of complex structures. The pattern-based multi-point geostatistical method SIMPAT has insufficient efficiency in extracting data patterns and calculating their similarities. This paper proposes a multi-point geostatistical method based on the cluster method (CMMS). The basic idea is to define two types of templates, scanning training image through the large template to extract the data pattern, and use the small template to reduce the dimension of the data pattern. For discrete variables, the facies with the largest number of occurrences in the data pattern extracted from the large template is taken as the facies type of the corresponding small template. For continuous variables, the average values of variables of each grid in the data pattern are taken as the values of corresponding small templates. Similar patterns can be grouped into one group by dimensionality reduction through small templates, which has a high fidelity of information contained in data patterns extracted from large templates. In the simulation, data events are compared with clustering pattern representation to find the most similar pattern, and then the most matching data pattern is found in the selected pattern class. By two times comparison, the number of similarity calculation is greatly reduced. The results of simulation, calculation time comparison and statistical feature reproduction show that the computational efficiency of CMMS algorithm is 30-40 times higher than that of SIMPAT. The simulation results of CMMS can well reproduce the geological model and statistical features in training images, and this method can be directly applied to continuous variables simulation.
In the eastern Sichuan Basin, the oil and gas show is good in the sandstone of Silurian Xiaoheba Formation, but the exploration and development have not made great breakthrough. In this paper, the microstructure of Xiaoheba Formation sandstone was studied by means of thin section identification and scanning electron microscopy. The solid asphalt and nano pore network system of asphalt were found in Xiaoheba Formation sandstone. Based on the comparative analysis of the characteristics of tight sandstone gas accumulation in Canada，three conclusions are put forward. In addition to primary pores and secondary pores, the sandstone of Xiaoheba Formation also develops solid asphalt network and solid asphalt nano pore network system. The nano?pore network of sandstone asphalt in Xiaoheba Formation is derived from the secondary cracking of liquid hydrocarbon charged in the early stage. The natural bubbles formed by the secondary cracking are solidified to form the asphalt nano pore network. The regional development of the asphalt nanopore network is controlled by the sedimentary microfacies, sand mud assemblage, reservoir formation and evolution process. The sand mud inter?bedded stratigraphic assemblage is conducive to the formation of the asphalt nanopore network, which has great exploration value. The research results are of great significance to improve the geological understanding of the Xiaoheba Formation reservoir in eastern Sichuan and guide the exploration of natural gas.
It’s very important for the development of shale gas reservoir to describe the adsorption characteristics of shale gas reservoir, especially at high temperature and pressure and predict adsorption isotherms under different temperatures by one adsorption isotherms. Based on the D-R adsorption potential method, isothermal adsorption curve under high temperature and high pressure was established, which can predict the isothermal adsorption curve under different temperature. The method is fitting of the real data in Ordos Basin, with pressure from 0-30 MPa, and temperature at 120 ℃, and forecast their isotherms under 20-100 ℃. Results show that the temperature has no effect on the maximum adsorption capacity, only affect the change rate of absolute adsorption capacity with pressure, but the temperature will greatly affect the maximum amount of excess adsorption and the downward trend at high pressure.
The natural fracture and regional geostress determine the fracture propagation together, which makes it difficult for conventional methods to predict the fracture propagation direction in different positions. But the four-dimensional fracturing monitoring results are used to constrain ant body tracking technology, and then to predict the stress weak point, which can indicate the direction of fracturing grow. 172 stress weak points are identified via 51 layers, use the improved ant tracking method to match them by adjusting the parameters such as initial boundary, tracking deviation, illegal step length, legal step number and stop standard. The results are applied to verify the fracture zones of 5 newly monitored vertical wells and 2 horizontal wells, and the fracture trend is consistent with the prediction results, and the complexity of the predicted result has a good correlation with the productivity of the fractured wells. It shows that the fracture trend distribution predicted by this method is accurate, which provides reliable support for later complex fracture fracturing and well location deployment.
There are some tight sandstone reservoir accumulations vertically in Linxing area, the understanding of gas and water distribution regularity and controlling factors is unclear, which result in the restricted progress of natural gas exploration and development in the area. Water chemical analysis showed that tight sandstone formation water is CaCl2 type, the gas reservoirs were not destruction on a large scale. We found the occurrence of formation water is controlled by pore type and pore structure through rock slice analysis and nuclear magnetic experiment, the free water mainly exists in intergranular pores and dissolved intergranular pores, capillary and bound water mainly exists in dissolved particle pore and intercrystalline pore. Gas and water distribution is mainly influenced by gas-generating intensity, passage system, amplitude of structure and reservoir heterogeneity. The reservoir has more free water when it is far from the source rock and conducting ability of fault is weak, and under certain structure amplitude exists the possibility of gas water differentiation. Well deployment, commingled layer production and drainage rules should be optimized according to the gas and water distribution regularity during the process of gas field development.
Tight sandstone gas reservoirs have large differences in physical properties and their uncertainty seriously restricts the stable production and efficient development of gas reservoirs. In order to effectively develop the unutilized reserves of tight sandstone gas reservoirs and improve gas production and recovery, it is necessary to optimize well pattern density of tight sandstone gas reservoirs with complex reservoir conditions. By analyzing the effects of seven reservoir physical parameters on single well dynamic control area, including permeability, porosity, effective thickness, water saturation, threshold pressure gradient, productivity coefficient and storage capacity coefficient, the relationship between reservoir physical parameters and single well dynamic control area without interference between wells is inferred by using fuzzy mathematics method. The calculated fuzzy prediction value of the single well dynamic control area is compared with the geological well control area to determine whether there will be interference between wells after the well pattern is encrypted under different reservoir physical conditions, and the interference probability curve that changes with the well pattern density is obtained. Furthermore, a recovery evaluation model is constructed based on the inter-well interference probability, which is applied in Su 6 well area. The results show that using the new evaluation method for tight sandstone gas reservoirs, the average cumulative gas production per well and recovery evaluated through the physical properties of the reservoir are consistent with the actual production dynamics results. Under certain conditions, this method is reasonable and reliable. The new method of recovery evaluation provides new ideas for well pattern optimization of tight sandstone gas reservoirs.
Volcanic oil and gas reservoir is one of the most difficult reservoirs both domestic and overseas. In recent years, the proven petroleum geological reserves of the Carboniferous in the northwestern margin of the Junggar Basin are 140×106 t, and large-scale production capacity has been built, laying a good foundation for the development of Carboniferous oil and gas reservoirs. Well Jinlong 10 which is in the northwestern margin of the Junggar Basin is a typical Carboniferous volcanic reservoir. Its reservoirs are characterized by extensive lithology, complex pore structure and strong heterogeneity. Ensuring the characteristic of studied reservoir has a good guiding role for studying later part of production capacity controlling factors and distribution. Based on the static data such as drilling, logging and core samples, it has been found that the reservoir space is mainly composed of dissolution pore and secondary fracture. The reservoir capacity characteristic has been carried out by production monitoring, oil test and other dynamic data in this paper. Four types of production capacity has been yielded including: stable production, bottom water cone into the liquid stable type, capacity failure type, no capacity type. The results show that the oil well productivity is mainly controlled by factors such as pore-fracture development, tectonic location, bottom water and fracturing scale.
M Oilfield is the first gas cap reservoir in the East China Sea, which has complex driving energy. Its seepage mechanism and development technology policy are essentially different from conventional reservoirs. Aiming at the difficult problem of effective development of this kind of reservoir due to the contradiction of gas channeling, oil invasion and water invasion, the technology of stimulation measures is studied. At the same time, three innovative technologies have been formed: splitting method of variable gas oil ratio phase production based on production time variability; a new method for calculating water displacement efficiency of water drive gas condensate reservoir with bottom oil; prediction technology of dynamic oil displacement contribution index under net driving energy. These technical achievements can provide important reference and technical support for the development of similar complex reservoirs such as gas capped reservoirs or condensate gas reservoirs with oil rings.
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