| The past 10 years, with the development of computer hardware and software technology, reservoir numerical simulation technology has become an indispensable reservoir engineering and evaluation tools of oil and gas field development,which can better simulate the complex mechanism of liquid flow in the reservoir and remaining oil distribution, development schemes. Now this technology has played an important role in oil and gas field development.Fractured-cave carbonate reservoir space is consisted of a large cave (0.5m-5m), cracks and pores,which maks it has large diversity, different scales and complex flow patterns. The flex flowings of stream flowing in caves, Darcy flowing in dissolution pores, two dimensional high speed flowing in cracks make the numerical simulation of this "complex media" difficult.which is not reported at home and abroad.The main problems are as flows. (1) Existing reservoir simulation techniques are based on porous continuum theory and the key are the Darcy equation and equation of continuity,so it is needed to develop new mathematical models of fractured-vuggy reservoir in complex media. (2) Seepage is flowing in the solid matrix flow and cave stream is flowing within the cavity, which make it difficult to bulid and solve the coupling equations of interface (3)The function and influence of oil and water in caves and the vadose zone is greatly diffferent,which make it difficult to simulate the mulitphase flow of reservoir. (4) The relationship of flowing velocity and pressure is not explicitly requiring solving pressure and 3-way speed, which make the solving greatly difficut.Research ideas:On the basis of description and mathematical abstraction on fractured-vuggy reservoir media, mathematical model suitable for fluid flow in fractured-vuggy reservoir is built. The comples flow equations on the stream flow in caves,seepage in pores&vugs and interface flow are established based on the couple method between stream flow and seepage. At the same time, considering the limite of computer speed and resource, on the basis of multi-medium flow theory numerical simulation method of reservoir seal is built: dealing with separately the large cracks and cave, Darcy or high speed non-Darcy seepage flow calculation in pores& vugs and mesh cracks. This numerical simulation method reduces the amount of calculation and ensure accuracy. Finally, A numerical simulator is programed and applicated in target zone Tahe oilfield.Main research achievement:(1) Establishing the coupled numerical simulation method for fracture-vug type carbonate reservoir, analyzing the characteristics of fracture-cave reservoir,proposing the coupling simulation scheme of the continum media and discrete media, buliding a coupled mathematical model,which solve the flowing key problems:couple of interface of stream flow and seepage,interface tracking of two-phase flow in caves. By decoupling the flowing border and simultaneous solution of the algorithm, a coupling method of numerical simulation on fracture-cave is formed. (2) Developing the theory of numerical simulation of multi-media, establishing the numerical calculation method of cave streamand multiple media complex streams, which solve large-scale reservoir numerical simulation effectively. The discrete nonlinear algebraic equations is solved by using Newton-Raphson method or implicitly Adaptive implicit method (Adaptive Implicit Method, known as AIM). The equivalent numerical simulation of fracture-cavity reservoirs based on multi-media methods is formed. (3) A reservoir numerical Simulator (KarstSim software) of the equivalent multiple media,which can solve the problem of three-dimensional numerical simulation of multiphase flows in complex medium.is formed.This simulator implements the calculation of Darcy flow and non-Darcy high speed of multi-phase fluid flow in multiple media and the multiphase flow equivalent method in caves. The complex medium of the simulator can simulate include caves continuous medium. The continuous medium are as flows:pores&vugs,dissolution pores, matrix ,large-scale fractures, network of cracks, micro-cracks.The complex flow are as flows:Darcy, low-velocity non-Darcy flow (heavy oil), high speed non-Darcy flow, pipe flow, fracture flow. (4) According to the actual production, this article proposes the pattern of waterflooding in multi-well fracture-vug units. This article researches the injection development mechanism in fractured-cave carbonate reservoir by using the reservoir numerical simulation means of complex media and puts forward the injection development mode on different time and formation. ① The aim of early injecton is to supplement the formation energy and water-floodtime .when the pressure reaches the original reservoir pressure by waterflooding, according to the mositure rising law of effectly oil well, the mode of injection to enlarge the sweep area and pro vent the intected water coming into is established. ② According to the different layers and the combination mode of fracture and cave, this article establishes the injection-production mode: production in caves and injection in fractues, production in the upper and injection in the low. ③ In the process of injection development, we need to understand the degree of connectivity between wells, to grasp the magnitude and direction of water flow ,to determine the injection and production parameters according to the results of tracer test, which can reach the purpose of increasing the water spread area. After injection adjustment in S48 fractured-cave unit, the cumulative incremental oil production is 31.8x104t. Development model has been applied widely and effectively guides the of the waterflooding in Tahe oilfield.Main innovations:(1) According to the characteristic of diversity reservoir and flow complex of fractured-vuggy reservoir ,a coupled mathematical model of multiphase fluid flows between seepage in complex mediaum(Darcy flow, high speed non-Darcy flow) and cave stream. (2) This article forms the coupled numerical simulation technology. Establishing the coupling numerical methods of two-phase flow interface in cave and between caves and pores., writing a computer program. (3) This article forms reservoir numerical simulation techniques of equivalent multiple media. On the basis of multiple media theory, numerical computation method of multi-media including cave stream is formed and a computer program is wrote. (4) This aticle proposes a "spatio-temporal difference" waterflooding development mode of fracture-vug units which has been applied widely in Tahe oilfield. |
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