The Study On Small Structure And Remaining-oil In Complex Fracturing Oilfield

This paper is to deal with two problems: one is the lack of the study and summarize of small structure description in complex fracturing oilfield, which is one of the important controlling factors of remaining oil unit of old oil-field in our country; the other is the lack of understanding on the cause of the remaining oil about old oil-field in substance, and there is no effective unit-partition mode. Especially the new types and fields of the remaining-oil unit are discovered recently. On the basis of the theories of seismology, sedimentology, tectonics, petroleum geology, seepage mechanics, reservoir engineering, by use of the abundant practical data of seism, well-drilling, well-logging, development, measuring, the study on small structure description and remaining oil in complex fracturing oilfield are developed. Firstly, take the example of complex fracturing oilfield in Dongying depression of Bohai basin, by establishing geology-seismic reflection model of small-structure and combining the theories of oscillation of seismic event, three-dimension seismic theory and practical distinguishability of small-fault are analysed. Following results are received: â—‹1 the theoretic distinguishability of small-fault in Chunhua oilfield is 24.0m, but the practical distinguishability in three-dimension section can reach 10m, and the evidence that the plane distribution and change characteristic of small-faults drilled by a few wells are ascertained by tracing three-dimension section.â—‹2 the small-faults that are distinguished by three-dimension seismic section are reliable, which can offer the evidence that the plane distribution and change characteristic of small faults drilled by no well are ascertained by tracing three-dimension seismic section, and its distance is about 10m; â—‹3 the analysis results of distinguishing degree and reliability of small faults in vertical three-dimension section offer the evidence that the fault points are demarcated by use of three-dimension seismic data.â—‹4 the length of small faults and small structures (Chunhua oil-field )in landscape orientation are 650m, its size corresponds with the smallest unit in injection-exploiting (about 300m), so the evidence of the injection-exploiting regulation measures in practical production are provided. The studies of small structure's distinguishability, offer the basis and support for establishing the study mode of small structure in complex fracturing oilfield. In the three-dimension sections, on the basis of the small structure theory and the analysis of practical distinguishability , for the example of the development of complex fracturing oilfield(such as Chunhua oilfield) in Dongying depression of Bohai basin, by use of the data of three-dimension seismic, well-drilling and productions, this paper has systemic analysis on the small structure in complex fracturing oilfield, and sum the basic mode, then set up the fine structure mode of Chunhua complex fracturing oilfield. So the problems of structures that have not finished for more than twenty years are solved; at the same time, the small structure unit that is the necessary condition in the study of remaining-oil distribution are marked off. These offer the framework and goal of the description of economic and exploiting area. The mode can guide the fine structure study in eastern complex fracturing oilfield. Secondly, on the basis of the study on the small structure system and mode establishing in complex fracturing oilfield, this paper has the systemic study on the remaining oil distribution laws. The practice of development show that: on the middle-later phase, the emphasis of development geological study is the description of economical remaining oil distribution; at present, the main theory(or viewpoint) is the positive small-structure controlling remaining oil, and the main means are the technology of reservoir fine description. By the fine description of the reservoir static states characteristic, the distribution of remaining oil is studied and described. This can offer the evidence of practical measures and ways by which enhance the recovery ratio or improve the development effect. However, the practice of development and the systemic study on remaining oil show that: the distribution and accumulation laws of remaining oil are controlled by the static and dynamic factors. On the course of accumulations and exploitation of oil-gas, the fluids always accumulate according to the theory of potential controlling, the moving directions of oil, gas, and water always are from the higher potential area to the lower area. So the static factors (especially the structures of reservoirs) make the boundary of the movements of oil, gas and water or the energy functions. On this basis, searching for the energy balancing area or the local energy balancing area in the non-balancing states is the basic ways to study and research the remaining oil accumulation units. The results of research show that: the relative low potential close area is the necessary condition that forming the economic remaining oil, and the basic unit that remaining oil possibly distributes and accumulates; but if we only consider the simple static factors of positive small-structure, wecan not rationally explain the new types and areas in the practical developments. Considering this, we summarize the laws of remaining oil distribution and accumulation, and put forward the theory of potential controlling remaining oil, and classify the remaining oil to 3 kinds and 9 types. So we get rid of the bind of the theory of positive small-structure's controlling on the remaining-oil distribution and accumulation, and spread the domain and direction of old oil-field's excavation. At the same time, according to the theory of potential controlling on remaining oil, we set up the mode of "dynamic accumulation and generation to form new reservoir",and offer the theoretic basis for the study of remaining oil and spreading the practical domain. This have important tactic significance on the excavation and enhancing the recovery ratio in the last phase, especially the regulation on the high water-cutting low effect reservoirs, and on the production ability resume and redevelopment of waste reservoirs. By use of the above study results, in the exploitation of complex fracturing and low permeability Chunhua oil-field ,and the south area of high permeability Liangjialou oilfield and other small reservoirs, we gain the good results of application.