| Ordos basin is the second largest sedimentary basin in China, which belongs to craton superimposed basins with abundant oil and gas resources. The reserch area in this paper,Bai209, is located in the southwest of northern Shanxi basin, sloped and affiliated to Changqing Baibao Oilfield.Its main oil layer is Yanchang group6oil-bearing reservoir of the Traissic. Bai209is a typical special low permeability reservoir.In this area, the average porosity is11.1%and permeability is0.47×10-3μm2.Through decades of exploration and development.Changqing oil field has basically formed a set of methods and experience of low porosity and low permeability reservoir description.They accumulated abundant experience in oil field geology, reservoir engineering, laboratory analysis and other technical studies,but there is lack of effective methods to judge the fracture direction of low permeability reservoir, which leads to many issues, such as low efficiency in reservoir water flooding, water raise fast, and increasing difficulties in stable production.Focusing on above problems, the paper adopts quantitative statistics and qualitative description approaches to carry out in-depth research on low permeability reservoir fracture prediction of Chang6layer. On the principle of maximum extent to single factor analysis, guided by reservoir sedimentation, geochemical and geological reservoir development and theory with many kinds of dynamic and static monitoring methods,It include ancient tectonic stress field, reservoir characteristics,geochemical characteristics of crude oil,water flooding front, interference well test, tracer, water injection profile and so on. Meanwhile, on the basic of comprehensive fracture prediction achievement, focusing on water injection influence of reservoir fractures. Make development measures of efficient and reasonable development for the next step in this block.Through the research, this paper obtains main achievements as following:(1) According to background of Ordos basin’s regional sedimentary, Bai209is located in the southwest of northern Shanxi basin slope, This paper focuses on one stage of Chang6reservoir, which begins to shrink, rapidly depositional development. The research block has characterized with low energy, low permeability, low porosity and low productively.(2) Tectonic stress is geological body internal force of per unit area caused by external force.The evolutional ancient tectonic stress field controls the formation and distribution of naturally fractures in low permeability reservoir, but current tectonic stress field affects natural fractures preservation situation and seepage rule.Through estimating of ancient tectonic stress field and tests and analysis of current tectonic stress field,it got that the maximum principal stress direction for this area is NE73°～NE79°.The direction of north-east exists between natural and artificial fracture, and they are main open fracture.(3) The degree of development of the reservoir fractures, distribution patterns is influenced by a variety of geological factors such as the reservoir structure, lithology, thickness, and microfacies.It develop nose structure in Chang6layer of Bai209, especially in the layer of the high point, ups and downs of the layer and the large change of the structural curvature of the central and east, coupled with the reservoir has a slump causes the bottom of the lake turbidite fan depositional systems, structure, low maturity of the composition, thin reservoirs, small particles of rock, brittle, indicating that the research block can develop fractures easy,(4) The same cause of the crude oil, it also keep a degree of similarity, it embodied in the chemical composition and characteristics of family. As the faults of the reservoirs and seal separating function, there is variance in composition and content of the compounds in different crudes. Through the analysis and comparison of different crude oil samples in chromatographic fingerprint parameters feature, after classification of crude oil,we found that the same types of crude oil has the possibility of connecting, showing fractures maybe existed between Wells; While different types of crude oil,reaserch results indicates that there is barrier between wells.Therefore, geochemical chromatographic fingerprint technology can be used to judge barrier between wells.Then,we can divided Bai209study area into①、②、③types. Between Type①、②crude oils, there is barriers; Type③is hybrid crude oil, the nearby area of mixed oil wells maybe fracture growth zone and fractures would more frequently be found in the similar type of crude oil.(5) The paper predicted well’s fracture direction and distribution by single factors comprehensive reaserch results, Production data and water flooding front, interference well test, tracer, water injection profile and dynamic monitoring data analysis.In sum:the property of prosity and permeability is better in east area of Bai209block, micro fractures are developed, belongs to porous-fracture type reservoir, reservoir is seriously waterflooded in this area; the reservoir of middle area is in poor connectivity, low liquid-producing capacity, high water cut. It belongs to the porous-fracture type reservoir; the western of the reservoir is not waterflooded and with low water cut, belongs to pore type reservoir, fractures are developed.(6) The co-existing artificial and natural fracture to produces various impacts on water injection development in Bai209area, on the one hand, the fractures link up seepage channel of low permeability reservoir, increase seepage area, improve the well productivity;On the other hand, as fractures existing, cause injection water are easily flows along the fracture,destroy injection-production balance, leads to water flooded in part of the wells, and some wells water injection does not work for long-term.(7) Through the reservoir engineering relevant knowledge, to discusse the water injection development features of common fractures developed in Bai209block,and found that:①in this area,total water cut is still not very high, overall development effect is good, but the water cut will increase year by year, later period exploitation is more and more difficult;②The water cut rising-rate variation range is:-4.95-12.77%in the area, as mining proceeding, it also increases by degrees;③In Bai209block, it calculated the recoverable reserve for170.36x104t,geological reserves for920.59x104t, the ultimate recovery is18.5%by using Np-logWOR water flooding characteristic curve.lt can improve the development contradictions through development adjustment.On the basis of combination of the sedimentary geology, crude oil production and the geochemical characteristics, dynamic monitoring of fracture the forecast method, and summarized the fracture distribution of research block, and understanding of fractures on the water injection effect and the present block of characteristics of water injection on the basis of understanding,.This paper shows a series of improving measures to solve development contradictions of fracture developed area,such as:(1)for some groups of partial water cut up fast or high water cut production in the block at present,and carry out water shutoff profile control and suitable plugging agent sealing the water injection and the oil leak or high seepage channel to improve the interlayer contradictions;(2)for the other groups,implement moderate water injection to prevent water injection pressure is too high for which leads to water channeling;(3) increase daily water-injection rate and intensity of fracture line, or closed down,change channel of high water cut production line, thus change the water flooding into the direction, expand the injection water affected area;(4) The wells that are poor porosity and poor permeability or the wells are difficult to improve water injection production in long-term, they can implement selective temporary plugging acidification、fracturing and fill holes and other measures to improve water injection, improve the layered reserves producing status. |
PDF Full Text Request