Research On Water Coning And Artificial Interlayer Control Coning To Enhance Oil Recovery Mechanism Of Bottom Water Reservior

Bottom water reservoir accounts for a large proportion of reservoir in China , the reserve is very rich. With oil fields go into secondary production or the third exploitation, the development characteristic of more fields inclines to bottom water types, except a large number of natural bottom water reservoir. The characteristic of bottoom water reservoir is that all the oil-bearing area contacts with the bottom water, this is the bottom water reservoir is superior to other reservoirs in development respect, but also the development of bottom water reservoir where the difficulty lies. On the one hand, the area which reservoir contacts with bottom water is large, making the capacity of bottom water intrudes into reservoir enhanced greatly, the consumed formation energy to exploit crude oil can be replenished from the bottom water in time, most of the development of bottom water reservoir have demonstrated the characteristics of sufficient energy, but on the other hand, the presence of bottom water brought a serious water production problem for oil well, we can usually see the following characteristic in production process: early water breakthrough, short water free oil production period, water cut rises fast even flooding after breakthrough, which result in lower recovery ratio, increase the risk of exploitation. In order to develop the bottom water reservoir reasonably, decline production cost and risk, strengthen the control for bottom water coning, we need to deepen the study of bottom water coning regular pattern. In this paper, the author does a large number of research on the bottom water coning mechanism and stable production and watercut control at home and abroad, basis on the previous work, studies the coning mechanism of bottom water reservoir vertical wells, horizontal wells and bottom water gas-cap reservoir horizontal wells, and bases on the coning mechanism, carries out the study of artificial interlayer stabilizing oil-water-control mechanism, the research fruit this paper obtained are as follows:In the study of bottom water reservoir vertical wells coning, supposed the upper section of perforation interval is radial fluid flow, the lower segment is a gradual transition from the radial flow to a spherical flow, namely, the seepage flow fluid from distant formation to the near wellbore area is radial flow, and the seepage flow fluid from near wellbore area to the bottom of well is hemispherical flow. In the calculation, the total output is divided into radial flow and spherical flow yield. Three kinds of situation of original oil/water interface as a boundary condition is proposed in the bottom water model, are: the original oil-water interface is constant pressure boundary, the pressure is equal to the original reservoir pressure of the initial exploitation; the original oil-water interface is constant pressure boundary, the pressure is equal to the pressure of supply boundary during the development; the original oil-water interface is a variable pressure boundary, the pressure varies with the time and horizontal distance. Depending on the different boundary conditions, the author established the mathematical model of water cone height, critical production, water cone shape and at the bottom water breakthrough time calculation.Through comparative calculation we can see from the third hypothesis, critical production is relatively large and the water cone height is too small, this is mainly due to the limited understanding on the bottom water flows situation and pressure distribution on the oil-water interface, so there is a flaw in the hypothesis of original oil-water interface pressure. But for the reservoir bottom water energy is not sufficient, this assumption is practical, therefore, future research should focus on the bottom water flows situation and pressure distribution on the original oil-water interface. In the three kinds of boundary conditions, the second hypothesis is in line with most of the reservoir, so, in water-cone parameters calculation after the bottom water breakthrough, bases on the second boundary condition mainly, namely the original oil-water interface is constant pressure boundary, the pressure is equal to the pressure of supply boundary. By comparing the critical production obtained from Dupuit method, Schols method, Boyun Guo method and approach of this study can be seen that the critical output calculated by the method described in this article are in good agreement with other methods, this shows that the model obtained in this paper is more accurate in forecasting the bottom water coing. Analyzing the of critical production and water cone shape by using the model. Described the phenomenon of bottom water reservoir horizontal wells coning and analyzed the influence factors of horizontal wells bottom water coning. Established a series of formula for horizontal well ofthe bottom water and gas cap reservoirs, compared and analyzed the critical output and breakthrough time calculated. Calculating the corresponding theoretical plates, the best placement of horizontal wells in the reservoir can be acqired by the data calculation, as well as the breakthrough time.Fluid flow equation can be obtained from two-dimensional Laplace equation,and make use of the formation conditon of stable state water cresting, the critical output and breakthrough time as well as dimensionless cone height of horizontal well bottom water can be acquired. Based on the two-dimension, there is a more detailed formula derivation and demonstration for three-dimensional model. Then corresponding critical production, breakthrough time formula can be obtained. For a longer horizontal well segment and a larger oil drainage radius, only a simple numerical integration of trigonometric functions can analyze and calculate. This method is much simpler than other analytical methods. A simple relational expression can be obtained by calculating results, and can predict breakthrough time.Based on hydrostatic principles and movement law equation of fluid into the interlayer, established computation module of interlayer form in the case of the side slope of bottom water reservoir into artificial interlayer is a curve. The model quantitatively describes the relationship between interlayer height and production and reservoir thickness and radial distance as well as the reservoir permeability, crude oil viscosity, accorde to the model can derive the largest interlayer height, interlayer height of different radial distance and maximum extension length of the interlayer in the radial direction. Established a resolution method for bottom water reservoir water cone model, sumed the interlayer fluid is radial fluid flow and ignored non-Darcy flow, obtained the analytical solution of the model. Meanwhile analyzed the characteristics of the interlayer combined with field cases, compared the distribution regular of interlayer form in the following four situations: different injection volume, different interlayer viscosity, different injection rate and different permeability, which provides a reference for the development of bottom water reservoir.By means of the actual field data, and make use of numerical simulation method can verify the interlayer form in the case of different injection volume, different interlayer viscosity, different injection rate and the ability of stable production and watercut control, the results show that the calculation formula of interlayer from theory is correct, and the effect of increasing oil and rainfall is obvious.