A Comprehensive Model for Evaluating Coalbed Methane Reservoirs in China

Coalbed methane reservoir （CBMR） evaluation is important for choosing the prospective target area for coalbed methane exploration and production. This study aims at identifying the characteristic parameters and methods to evaluate CBMR. Based on the geological surveys, laboratory measurements and field works, a four-level analytic hierarchy process （AHP） model for CBMR evaluation is proposed. In this model, different weights are prioritized and assigned on the basis of three main criteria （including reservoir physical property, storage capacity and geological characteristics）, 15 sub-criteria, and 18 technical alternatives; the later of which are discussed in detail. The model was applied to evaluate the CBMR of the Permo-Carboniferous coals in the Qinshui Basin, North China. This GIS-based fuzzy AHP comprehensive model can be used for the evaluation of CBMR of medium-high rank （mean maximum vitrinite reflectance 〉0.5 %） coal districts in China.

Log identification method in complex sand reservoirs

In order to obtain effective parameters for complex sand reservoirs,a log evaluation method for relevant reservoir parameters is established based on an analysis in the gas-bearing sandstone with high porosity and low permeability,low porosity and permeability and on various characteristics of log responses to reservoir lithologies and physical properties in the Neopleozoic sand reservoir of the Ordos basin.This log evaluation method covers the Cook method that is used to evaluate the porosity and oiliness in high porosity and low permeability reservoirs and another method in which the mineral content,derived from geochemical logs,is used to identify formation lithologies.Some areas have high calcium and low silt content,not uniformly distributed,the results of which show up in the complex formation lithologies and conventional log responses with great deviation.The reliability of the method is verified by comparison with conventional log data and core analyses.The calculation results coincide with the core analytical data and gas tests,which indicate that this log evaluation method is available,provides novel ideas for study of similar complex reservoir lithologies and has some reference value.

Predicting gas-bearing distribution using DNN based on multi-component seismic data: Quality evaluation using structural and fracture factors

The tight-fractured gas reservoir of the Upper Triassic Xujiahe Formation in the Western Sichuan Depression has low porosity and permeability. This study presents a DNN-based method for identifying gas-bearing strata in tight sandstone. First, multi-component composite seismic attributes are obtained.The strong nonlinear relationships between multi-component composite attributes and gas-bearing reservoirs can be constrained through a DNN. Therefore, we identify and predict the gas-bearing strata using a DNN. Then, sample data are fed into the DNN for training and testing. After optimized network parameters are determined by the performance curves and empirical formulas, the best deep learning gas-bearing prediction model is determined. The composite seismic attributes can then be fed into the model to extrapolate the hydrocarbon-bearing characteristics from known drilling areas to the entire region for predicting the gas reservoir distribution. Finally, we assess the proposed method in terms of the structure and fracture characteristics and predict favorable exploration areas for identifying gas reservoirs.

Comprehensive Evaluation Model of Reservoir Operation Based on Improved Set Pair Analysis

A comprehensive evaluation model based on improved set pair analysis is established. Considering the complexity in decision-making process, the model combines the certainties and uncertainties in the schemes, i.e., identical degree, different degree and opposite degree. The relations among different schemes are studied, and the traditional way of solving uncertainty problem is improved. By using the gray correlation to determine the difference degree, the problem of less evaluation indexes and inapparent linear relationship is solved. The difference between the evaluation parameters is smaller in both the fuzzy comprehensive evaluation model and fuzzy matter-element method, and the dipartite degree of the evaluation result is unobvious. However, the difference between each integrated connection degree is distinct in the improved set pair analysis. Results show that the proposed method is feasible and it obtains better effects than the fuzzy comprehensive evaluation method and fuzzy matter-element method.

Pore throat structure and classification of Paleogene tight reservoirs in Jiyang depression,Bohai Bay Basin,China

The pore throat structure characteristics of Paleogene tight sandstone and sandy conglomerate in the Jiyang depression are studied using cast thin section,conventional mercury injection,constant rate mercury injection and micro CT scanning data,and a reservoir classification scheme based on pore throat structure parameters is established.The material composition and structural characteristics of tight reservoirs are analyzed by casting thin section data.The pore throat structure characteristics of tight reservoirs are studied by conventional mercury injection,constant rate mercury injection and micro CT scanning.Ten pore throat structure parameters are analyzed by cluster analysis.Based on the classification results and oil test results,the classification scheme of Paleogene tight reservoirs is established.The Paleogene tight reservoirs in the Jiyang depression have the characteristics of macropores and microthroats,with pores in micron scale,throats in nano-submicron scale,and wide variation of ratio of pore radius to throat radius.The permeability of the tight reservoir is controlled by throat radius,the smaller the difference between pore radius and throat radius,and the more uniform the pore throat size,the higher the permeability will be.The lower limits of average pore throat radius for the tight sandstone and tight sandy conglomerate to produce industrial oil flow without fracturing are 0.6μm and 0.8μm,respectively.Reservoirs that can produce industrial oil flow only after fracturing have an average pore-throat radius between 0.2-0.6μm,and reservoirs with average pore throat radius less than 0.2μm are ineffective reservoirs under the current fracturing techniques.Different types of tight sandstone and sandy conglomerate reservoirs are classified and evaluated,which are well applied in exploratory evaluation.

A comparative evaluation of 3 kinds of cecocolon urinary reservoir

Objective To evaluate and compare 3 kinds of cecocloln urinary reservoir. Methods Perm pouch, indiana pouch or detenial cecocolon reservoir has been performed for 37 patients. The outcome was evaluated by urodynamic and clinically. Results Good continence has been achieved in all patients with an appendiceal continence mechanism. The capacity and intrareservoir pressure of detenial cecocolon was significantly different from penn or indiana pouch 3 months postoperatively (P【0.01) whereas the difference became in no significant 12 months postoperativelly (P】0. 05). The intrareservoir pressure on contraction was lower with penn pouch. Conclusion The penn or modified indiana pouch is better and more ideal as a urinary reservoir whereas the detenial cecocolon pouch is technically simpler. 6 refs,1 tab.

Advanced fluid-typing methods for NMR logging

In recent years, nuclear magnetic resonance （NMR） has been increasingly used for fluid- typing in well-logging because of the improved generations of NMR logging tools. This paper first discusses the applicable conditions of two one-dimensional NMR methods： the dual TW method and dual TE method. Then, the two-dimensional （T2, D） and （T2, T1） NMR methods are introduced. These different typing methods for hydrocarbon are compared and analyzed by numerical simulation. The results show that the dual TW method is not suitable for identifying a macroporous water layer. The dual TE method is not suitable for typing gas and irreducible water. （T2, T1） method is more effective in typing a gas layer. In an oil-bearing layer of movable water containing big pores, （T2, T1） method can solve the misinterpretation problem in the dual TWmethod between a water layer with big pores and an oil layer. The （T2, T1） method can distinguish irreducible water from oil of a medium viscosity, and the viscosity range of oil becomes wide in contrast with that of the dual TW method. The （T2, D） method is more effective in typing oil and water layers. In a gas layer, when the SNR is higher than a threshold, the （T2, D） method can resolve the overlapping T2 signals of irreducible water and gas that occurs due to the use of the dual TE method. Twodimensional NMR for fluid-typing is an important development of well logging technology.

Exploration of Subtle Trap in Jiyang Depression

This article analyses the procedure of exploration of the Tertiary subtle trap in Jiyang depression and divides the Tertiary subtle trap into 3 types (lithologic reservoir, stratigraphic reservoir and fractured reservoir) and 8 groups, then summarizes the common feature and founding discipline of the subtle trap and finds 4 accumulating modes including steep slope mode, depression mode, center anticline mode and gentle slope mode. Its main exploration methods are explicated from the viewpoint of reservoir geological modeling, description of recognizing traps and comprehensive evaluation of reservoir and so on.

Evaluation of dolomite reservoirs in the Longwangmiao Formation,Lower Cambrian in Northern Sichuan basin,China

With the extended petroleum exploration of the carbonate reservoir in the Longwangmiao Formation,Lower Cambrian in Sichuan basin,looking for a new favorable exploration area is the primary task in current exploration.This paper focusing on the dolomite reservoir in the Longwangmiao Formation in the Northern Sichuan basin,will evaluate the reservoir conditions,including reservoir lithology,reservoir spaces,physical properties and other basic characteristics.Combined with sedimentary environment study and diagenesis analysis,the genetic mechanism of Longwangmiao reservoir in study area will be discussed.It indicates that the reservoir rocks of Longwangmiao Formation in the study area are composed of dolarenite and crystalline dolomite,and the main reservoir spaces are intergranular dissolved pores,intragranular dissolved pores and intercrystalline dissolved pores.However,most of dissolved pores have been filled with bitumen,which lead to the reservoir properties very poor,both the porosity and permeability are worse than that of central Sichuan basin,so the reservoir in the Longwangmiao Formation in the Northern Sichuan basin is low-porosity and low-permeability reservoir.During the Early Cambrian Longwangmiao period,the study was near the old-land,and the energy of sea water was not enough to deposit many grain shoals,which cause the sediments are small with lots of quartz and muds.Moreover,because lacking of large scale karstification in the late diagenesis,there isn't much dissolved pores and vugs develop in the Longwangmiao Formation.Some Intergranular dissolved pores and intercrystalline dissolved pores formed by the early atmosphere water dissolved exist as some reservoir spaces,but most of them have been filled with bitumen,which was residual when the ancient oil reservoir transformed.Above factors cause the Longwangmiao Formation in the Northern Sichuan basin become not a very favorable reservoir in Sichuan basin.

Sedimentary characteristics of tide-dominated estuary in Donghetang Formation (Upper Devonian), central Tarim Basin

The Donghetang Formation (Upper Devonian) in central Tarim Basin has been thought an important oil and gas reservoir since the abundant oil and gas resources were found in the wells W16, W20, W34, and other fields. However, the sedimentary environment of the Donghetang Formation has been disputed because it suffered from both tidal and fluvial actions and there were not rich fossils in the sandstone. After the authors analyzed sedimentary features by means of drill cores, well logging data, paleosols, and with SEM obseruations, three kinds of sedimentary environments were distinguished: alluvial fan, tide-dominated estuary, and shelf. Particularly, the sedimentary features of tide-dominated estuary were studied in detail. Besides, the authors discussed sedimentary characteristics of the Donghetang Formation which was divided into two fourth-order sequences and five system tracts. At the same time, according to the forming process of five system tracts, the whole vertical evolution and lateral transition of tide-dominated estuary were illustrated clearly. Finally, the reservoir quality was evaluated based on porosity and permeability.

Evaluation of Shale Reservoir Quality by Geophysical Logging for Shuijingtuo Formation of Lower Cambrian in Yichang Area, Central Yangtze

Taking the shale of Shuijingtuo Formation of Lower Cambrian in Yichang area as the research object,the shale reservoir characteristics are comprehensively evaluated and classified by fitting regression and formula calculation method in this study,using laboratory testing and geophysical logging data.The results show that the interpretation data of ECS(elemental capture spectroscopy)logging has a high correlation with the measured minerals data,which can be a good method to evaluate the minerals component of the shale.The calculated content of brittle minerals at the lower part of Shuijingtuo Formation is the relatively highest,generally more than 40%,which is the most favorable segment for fracturing.The correlation coefficient between the interpretation data of CMR(combinable nuclear magnetic resonance)logging and the result of laboratory porosity test is 0.97,which can effectively and accurately evaluate the reservoir porosity.The evaluation results show that the porosity of the lower member of Shuijingtuo Formation is generally greater than 3%,while that of the upper member is generally less than 3%.The lower segment is with the relative optimal physical conditions.There is a good correlation between the acoustic logging data and the gas bearing content testing results.A gas bearing content evaluation model is established.The results show that the gas bearing content of the lower 20 m shale is generally more than 2%,indicating that the lower part is a shale gas enrichment segment.Mechanical parameters such as Young modulus,Poisson ratio and brittleness index of shale reservoir are evaluated by using the logging data of P-wave time difference and S-wave time difference.The continuous 15 m shale at the lower part is with the relatively optimal low Poisson ratio,high Young modulus and high brittleness index,developing the optimum brittle condition.Based on the evaluation and classification of above parameters,the shale is divided into three types.The TypeⅠis the optimal,mainly located at the bottom.Its thickness is 8.5 m in total.The TypeⅡmainly develops at the middle part.The TypeⅢis the worst,mainly at the upper part.

Characteristics and Evaluation of the Shale Oil Reservoir in Upper Es^3 Inter Salt in Liutun Sag

Shale intercalations in salt deposits of the upper part of the third member of the Shahejie Formation （Es3） in the Liutun sag have industrial oil and gas potential. This article classifies and evaluates lithology, pore systems, porosity, permeability and pore characteristics using core logs, XRD, SEM, lab and log porosity data of shale reservoirs in the salt formation. The lithology of these reservoirs is complex as parts of complex salt rhythms composed of clastic, carbonate and eva- poritic rocks. Their rigid minerals contents and total organic carbon are high, the organic type is good, and the maturity of organic matter ranges from medium to low. There are strong overpressures and natural hydraulic fractures. Organic matter pores and matrix-related shale pores provide an apprecia- ble part of the permeability. Different methods of measurement, sonic logging and equivalent cycle counting-point are used to evaluate the different types of porosity and permeability. A preliminary evaluation of shale permeability has been made by using fracture data from cores and image logging, and it is considered that the organic nets composed of organic matter pores generated in the maturation stage of shale have greatly increased oil permeability. On the above basis, this article proposes classifi- cation criteria for the upper Es3 inter-salt shale oil reservoirs to provide a foundation for evaluating other shale oil reservoirs in this area.