| As starting up pressure gradient exists in low permeability reservoirs, water injection mode and injector producer distance affect not only waterflood control extent but also effective driving index. Driving pressure gradient is less than starting up pressure gradient and the part of oil layers can't be employed effectively when injector producer distance exceeds a fixed value. At present, qualitative analysises are carried out on relation between effective driving index, well pattern and well spacing, which are still lack of the quantitative analysises in deep level. This paper will launch quantitative studies on relation between flooding pattern, starting up pressure gradient and effective driving index, water drive recovery efficiency by the method of non-darcy flow numerical simulation and then proceed well pattern optimization coupled with economic evaluation.This work will take Daqing peripheral low permeability oilfield of Yushulin as an object of study, at first base geologic researches are carried out, including analyzing lithologic characteristic, physical property, pore structure feature, reservoir evaluation and fixing routine water displacement efficiency, it finds that effective radius of Fuyang oil layers flow matrix is between 0.25μm and 0.65μm, filtration and storage abilities are poor, expulsion pressure is high and the oil layers are hard to recover. For Fuyu oil layers, core samples displacement efficiency is between 16.48% and 38.70%, average value is 32.8% which is quite low. Later nondarcy flow laboratory investigations of low permeability cores are carried out by way of laboratory experiments to to survey and evaluate the relation between starting up pressure gradient and permeability, starting up pressure gradient will rise substantially with the decrease of permeability when permeability is below 3×10-3μm2. Analyze nondarcy flow mechanism of low permeability cores, establish a basic math model to describe nondarcy flow, then a three-dimensional and three phases nondarcy flow math model of low permeability is established, the finite difference method was used to solve the model, and a corresponding numerical simulation software is developed considering the conditions of rate-specified pumping, pressure-specified pumping, rate-specified injection, pressure-specified injection respectively. Quantitative research about influence exerted by starting up pressure gradient, well spacing, water injection mode on development effect and effective driving index is carried out by way of nondarcy flow numerical simulation of low permeability, simulation results show that as permeability rise from 1×10-3μm2 to 12×10-3μm2, starting up pressure gradient decreses from 0.4481MPa/m to 0.0377MPa/m and sweep efficiency rises from 0.00% to 76.53%, water displacement recovery rise from 0.00% to 24.29% when well spacing is 300m, sweep efficiency rises from 33.60% to 62.80% and water displacement recovery rise from 11.10% to 21.95% as well spacing shrink from 350m to 150m when permeability is 5×10-3μm2, different water injection modes have great impact on development effects. On this basis, the relation between low permeability oilfield water displacement recovery and well spacing density is established by way of reservoir engineering considering the influence exerted by well pattern disposition on waterflood control extent, effective driving index, analyze optimal well spacing density and well spacing quantificationally under conditions of different oil prices and different tendering practice to provide technical descriptions for well pattern optimization and adjustment. At last, this paper tales Dong 16 block of Yushulin oilfield as an example, well pattern optimization numerical simulation study is carried out, according to technology limit of well pattern optimization, four proposals are designed on the basis of the law of distribution of remaining oil under the condition of present well pattern, through comparing and selecting these proposals, the preferred proposal is applied to case study and good development results have been obtained. Obviously, the research method has theoretical and practical significance to well pattern optimization of low permeability oilfield.
|
PDF Full Text Request