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Analysis Of The Causes Of Low-porosity And Low-permeability Reservoir Of The Upper Wuerhe Formation In Wu District

Posted on:2016-02-04Degree:MasterType:Thesis
Country:ChinaCandidate:M J LiuFull Text:PDF
GTID:2180330464961946Subject:Mineralogy, petrology, ore deposits
Abstract/Summary:PDF Full Text Request
Oil and gas is stored in reservoir, looking for good reservoir is an important task for the oil and gas exploration in petroliferous basin. However, a lot of the reservoir is not so ideal, such as the low-porosity and low-permeability reservoir. Therefore, finding out the causes of low-porosity and low-permeability reservoir is one of the cores of the development of oil and gas. Based on sedimentary petrology and reservoir sedimentology theory, taking Wuerhe Formation in karamay oilfield as the research object, combined with core observation, logging interpretation, and comprehensive utilization of seismic data and experimental data analyses, we have researched the sedimentary facies, diagenesis, reservoir pore structure characteristics, fine reservoir description of the purpose layer and the controlling factors of low-porosity and low-permeability reservoir, then provide the theoretical basis for the later development of oil and gas.The reservoir in Upper Wuerhe formation in 5 district present obvious differences with other clastic rock reservoir, bringing a lot of difficulties to do reservoir research.There is unconformity contact relation between Upper Wuerhe formation and the overlying strata and lower strata. Upper Wuerhe formation can be divided into three strata:P3w3、P3w2、P3w1. Sediments of upper Wuerhe is generally thick, mostly sandy conglomerate, in addition, some sandstone and mudstone. Based on the study of structural features, the sedimentary rock lithology, color and well logging facies, the sedimentary facies are determined. There are alluvial fan facies and fan delta sedimentary facies in Upper Wuerhe formation.The alluvial fan facies is divided into 3 subfacies, which divided into 10 microfacies; The fan delta facies has 2 subfacies, which divided into 6 microfacies.The conglomerate and glutenite of 5 district is near source deposition, whose rock particles transportation distance are relatively close. The composition maturity and structure maturity of conglomerate and glutenite are relatively low. The separation and grinding of granule are relatively poor. The tuff debris particles of conglomerate and glutenite is high (tuff lithic content 46.53%), which resulting in the poor ability to resist compaction. In the early period of diagenesis, influenced by compaction, pore and throat quickly became smaller or disappeared, this is one of the main causes of poor reservoir properties. The fillings of clastic rock in upper Wuerhe Formation is dominated by clay (as the matrix) and laumontite and gypsum are the main cements. In the studied area, the major cementation style is contact cementation and pore cementation secondly.The compaction of 5 district is relatively strong, which has important influence on reservoir. Strong compaction result in close contact of glutenite particles in the research area, so line contact is the major contact style. Under the strong compaction condition in the study area, the plastic material and matrix band bend, the rigid particle break. The bending of sheet mica minerals, the deformation of plastic tuff particles formed by extrusion, grain filling chlorite matrix and shale strip bending deformation are commonly seen in thin sections. In addition, under the action of strong compaction, clay or plastic particles are pressed into the pores form pseudo matrix. Cements in the area are mainly calcite and zeolite, which plug the pores and cause the decrease of reservoir porosity and permeability. But on the other hand, feldspar and analcime cements are easily to be corroded and form dissolution pore locally, which can improve the reservoir porosity and permeability.The pores and fractures of upper Wuerhe formation are mainly:primary intergranular pore, residual intergranular pore, dissolution pore and cracks. Intergranular pore was the highest, accounts for 32.7% of total pore; Followed by intergranular dissolved pores and intragranular dissolved pores, which take 28.15% and 16.22% respectively of the total fissure value. There is a special reservoir space type in upper Wuerhe formation in 5 district, that is the gravel edge stitch (or interface seam). The formation of the interface seam is due to the shallow buried depth of sediments and the infiltration and filling of mud from upper sediments in sandy conglomerate and glutenite, which shrink in diagenetic stage. The content of interface seam is relatively high, reaching 9.87%. The reservoir pores and cracks combination classification of study area can be divided into five:the residual intergranular pore, dissolution pore type, mixed pore type, dense type and pore-crack type.The porosity and permeability of reservoir is poor in 5 district. The porosity is generally less than 15% and the permeability is generally less than 50×10-3μm2. According to the clastic rock reservoir classification standard, the reservoir of the study area is defined as low porosity and low permeability reservoir. Through the study of sedimentary microfacies and reservoir characteristics, we have found that the causes of low porosity and low permeability of the reservoir in the study area are sedimentary microfacies, diagenesis and micro cracks. The relationship between clay content and porosity is inversely proportional, the lower clay content, the higher porosity value. At the same time, the rock particles is coarser, the ability to resist compaction is stronger, physical property is relatively well. Based on the statistic values of porosity and permeability in different sedimentary microfacies, we have found that the reservoir quality of the main channel microfacies (including root fan main channel microfacies and fan of the main channel microfacies) is better, the average porosity is greater than 10%, the average permeability is greater than 20 X 10-3 μm2. The reservoir quality of physical channel micro facies, braided stream facies, braided river facies, underwater distributary channel microfacies is also good which are favorable facies belts. Strong compaction leads to the decrease of the content of the pore in reservoir and the pore compaction rate is about 80%. Cements plug the pores in the reservoir, which reduce the content of pore. Therefore, the cementation is also an important factor of the poor reservoir. On the other hand, the clastic particles and matrix and the fillings, including mineral quartz and silica cementation, dissoluted and generate secondary porosity, which improve the reservoir porosity and permeability. The development of micro cracks are also greatly improving the physical property of reservoir, especially the reservoir permeability, directly affect the reservoir and percolation capacity of oil and gas. Through the experimental research in field, we have found that the reservoir of upper Wuerhe Formation must be acid fractured in order to get higher yield. This also reveals the fact that fracture has important influence on reservoir permeability.
Keywords/Search Tags:5 district, Upper Wuerhe Formation, Low-porosity and low-permeability reservoir, Compaction, Reservoir characteristics
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