| BaoBei district in Baolang oilfield is located in Yongning town of Yanqi district, the Hui nationality autonomous county of Bayangol Mongol Autonomous Prefecture, Xinjiang Uygur Autonomous Region. It is a NW-SE direction arch structure, which is firmly controlled by lithology and setted on Baolang-Sumu northern structural zone, north of Bohu depression, Yanqi basin. Porosity of the reservoir is 12-14%, and permeability is 2.97-27.3×10-3μm2, which shows such kind of reservoir is of low porosity and low permeability. Natural energy of this reservoir is edge-water mainly. Resulted from early rapid development, the reservoir productivity decreases quickly at the present time, and the water cut is at a upper level. Because of complex oil-water relationship and bad disciplinary distribution of remaining oil, later remaining oil development is faced with many problems. Oilfield people expect to improve development effect and enhance oil recovery through small-scale well pattern adjustment or scattered remaining oil development using horizontal well technology. According to remaining oil development practice in oilfield at high water cut stage, the effect of remaining oil development is relatively good using horizontal wells, but it's established on high cost, high danger, difficult management and adjustment. So it's very necessary to make comprehensive evaluation to ensure enough economic benefits. Based on this key problem, that is, developing scattered remaining oil using horizontal wells, this paper is expected to provide some technical and economic index for the oilfield to make optimization and comparison in different programs, at the same time supply important theories and methods for the oilfield to make scientific decisions.This research takes representative low permeable and low porous reservoir of this area for research object, and comprehensively refers theories and methods of many subjects such as reservoir description, sedimentology, reservoir geology, reservoir engineering, permeation fluid mechanics, oil economics and so on in specific reseach process. Based on extensive survey, combining with a large amouts of dynamic, static and experimental information and research findings before, using experiential analogy, reservoir engineering, numerical simulation methods and experiment ways, this paper gains deep knowledge on characteristics of geology, development and seepage, ulteriorly make overall assessment from feasibility to economical efficiency to effectiveness on exploiting remaining oil using horizontal wells, simultaneously summarizes a set of thinking and methods for making work about optimization choice of target area and optimization design of horizontal well parameters.During the research process, this thesis primarily makes three achievements. Firstly, we should do much fundamental work before optimization choice of target area and optimization design of horizontal parameters, including implement of structure and sedimentary background, grasping geology and seepage characteristics of reservoir, explicit about development problems and dialyzing the generation and distribution of remaining oil. Overall, the sedimentary system is braided river delta, and there are many faults and cracks on the anticline. The reservoir is low permeable and low porous, with serious heterogeneity, and in which the seepage is non-darcy flow because of the existence of start-up pressure gradient (0.0245MP/m). Using the numerical simulation way, We find that there are much differences among oil sand bodies in this area. Many monolayers have large quantities of remaining oil such asⅡ12,Ⅱ21,Ⅲ22,Ⅲ11,Ⅲ12, whose remaining geologic reserves is above 50 X 104t. The main causes of remaining oil distribution are imperfect well pattern, sand bodies'pinch-out, faults incision and faults barrier.Now, single-phase steady seepage in pseudo-three-dimensional places in one well is the perfect seepage way to make reservoir engineering evaluation for horizontal wells in low permeable reservoir. We should choose proper seepage solution to lead later work, then we should successively do optimal choice about reservoir type, layer series of development, oil sublayer and well area before flow potential and economic assessment to finish feasibility to economical efficiency evaluation work of horizontal well scheme. The optimal place we choose for horizontal well design is in B6-6—XZ1—B5-6—B1205 well area. If we designs a horizontal well, that is H5, in this area, initial production capacity is about 8t/d when the horizontal segment is 200m, which is larger than the economic limit initial production capacity which is 5.5t/d. After finish the feasibility and economic evaluation work, we should do optimization design of some important parameters of horizontal well and prediction of development index to finish effectiveness evaluation work of horizontal well scheme. Through the optimal design process, we can give some standards of horizontal well's parameters. Firstly, the optimal vertical location of the horizontal segment is 1/3 of the sand body thickness to the top, the horizontal location is parallel to structure lines, and the length is 200m. Secondly, the optimal well pattern is irregular 5-spot area pattern. Thirdly, the optimal well completion way is single perforated completion, wire wrap screen pipe completion included. Initial production capacity of horizontal well in this area is 20m3/d and initial production index is 10m3/d/MPa, applying numerical simulation, more favourable than vertical well. Then we can draw a significant conclusion that it's feasible and economical and effective to develop scattered remaining oil using horizontal wells in this area.Flow unit is one of important methods used in reservoir assessment, which shows a reservoir belt that is similar in lithology, petrophysics characteristics, and that is continuous and homogeneous in vertical and aclinic directions. This paper creatively builds relationship between FZI, that is, latent parameter of flow unit and both start-up pressure gradient and relative permeability principle, as expands the application of flow unit and lays a basis for flow uint to use in development evaluation and prediction. Besides, this paper systematically puts forward to a set of thoughts and methods to design horizontal wells in low permeable reservoir, and makes extension on horizontal well optimization to a certain extent. These achievements and conclusions have crucial directive function for low permeable oilfield to develop remaining oil using horizontal well technology. |
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