The Study On Water Flooding Characteristics And Corresponding Development With Bottom Water Reservoir

The main characteristic of the bottom water reservoir exploitation is bottom waterconing. Water coning leads oil wells to produce water in advance, and a sharp rise ofwater cut after producing water. It is easy for the wells to form a burst water floodingor even stop production. After the formation of the water cone, it is hard to consumerthe cone, and which reasonable method to take to inhibit the bottom water coning isthe key factor to influence the ultimate recovery of the bottom water reservoir.Therefore, it is crucial important for the reasonable exploitation to research theflooding law and controlling water development policy of the bottom water reservoir.The Y2reservoir is a low-inclination and faulted anticline layered edge waterreservoir. The northwest strata of Y2reservoir are flat. It has a wide area of oil-watertransition zone. It performances the bottom water characteristics: the oil stay up thewater reservoir, showing the producting laws of the bottom water reservoir. Thesoutheast layer is steeper, showing the side water reservoir characteristics.The crudeoil density and viscosity are low. The reservoir are low porosity and low permeabilitysandstone reservoir. The main types of the sedimentary microfacies are channeldeposits of braided river delta.The oil wells in the northwest of Y2reservoir have short anhydrous oilproduction time and the shapes of the water cut curves are convex. The water cutascension law showes the significant bottom water coning characteristics. Now, theaverage water cut of wells has go up to96%. There is little effect for water injectionto inhibit the bottom water coning. The recovery of the reservoir is only8%at present.When the pressure drop near the well bottom is greater than water and oil gravity difference, the bottom water will cone. When they are equal, water cone will stability.This study use mathematical methods and reservoir numerical simulation method toresearch the water cone shape. The shape of water cone is similar to a bell.The flooding characteristics research are mainly about the study of water coningcritical production and bottom water breakthrough time of vertical well and horizontalwell. The research methods are engineering calculation methods and numericalsimulation methods. Reservoir sedimentary rhythm, reservoir anisotropy, barrier andinterbed, reservoir thickness, the volume of the bottom water, oil&water viscosity,oil&water density, well space, fluid production and injection, open degree of thewells, the length and the vertical position of horizontal segment, exploitation methodsare all main impact factors to bottom water coning. The main reasons of bottom waterconing is the too large production rate at beginning, improper perforation, the bigratio of vertical permeability and horizontal permeability, the thick oil-water transitionzone, the small oil-water density difference and the thin oil layers.The corresponding development policy mainly focus on the clapboarddevelopment and horizontal well development. This study first study the inhibitoryeffect of the artificial barrier to the bottom water cone. Then, calculate the criticalproduction and water breakthrough time of the bottom water reservoir with theclapboard. And discuss the impacts of the clapboard radius, partitions and the opendegree of the reservoir above to them. This study suggests that the minimal clapboarradius is30meters and the bigger the better. The best distance between the clapboarand the oil-water interface is1/5times of the oil layer thickness. And the open degreeof the layer above the clapboard is0.7. The just time to plug is the time of inflectionpoint position of the water cut curve, which is generally at the time of when the watercut is30%-35%.The study discusse the types and the distribution of the interbeds and theinfluence to the bottom water coning. The natural interbeds of the Y2reservoir couldbe specificly divided into two major types by lithology. One is high gamma interbeds,another is high resistivity interbeds. High gamma interbeds have two types: muddyinterbeds and matrix interbeds. High resistivity interbeds are also divided intocalcareous interbeds and dense interbeds. This study statistik and analysis theinterlayer thickness distribution and the interbeds frequency distribution and densitydistribution. The trend between the interbeds frequency distribution or densitydistribution and the water breakthrough time is positive correlation. The greater thefrequency and density the longer the breakthrough time. Exploiting bottom water reservoir by horizontal wells has obvious advantages.Horizontal well can improve the anhydrous total oil production and have higherextract capabilities than vertical well. The geology and reservoir characteristics ofthe northwest of the Y2reservoir are suitable for using the horizontal wells. The paperoptimizated the reasonable parameters by the reservoir engineering calculationmethods and numerical simulation methods on the base of the current well network.The reasonable length of the horizontal segment is210m. The optimal verticalposition of horizontal segment is0.8-0.9times reservoir thickness distance fromoil-water interface. The plane position should be preferred based on the distribution ofremaining oil and reservoir structure. The reasonable well production of horizontalwells are20square/day. When the water cut is greater than92%, it is just time toconsider the extract.There are some other commonly used methods of controlling water drainage, likeoil production with water drainage method, the oil and water downhole separationmethod, the pressure cone method, the gas injection method, electromagnetic heatingmethod, injection water, polymer, oil-water emulsions, foams and air from injectionwells methods, and so on. But each method are not suitable for it very much.