Research On Reasonable Drawdown Pressure Of The Low Permeability Reservoir

Aiming at lack of systematic calculation in inflow performance relationship curve(IPR) at the low permeability reservoir, considered the complexity of reservoir physical property,porosity and permeability, some formulas for high permeability reservoir are not suitable. In the case of Gao 89 block in Chunliang oil field, a series of lab reseach and analysis in data indicate the average stress-factor of Gao 89 block is 0.03, the threshold pressure radient is 0.058MPa/m. A lot of curves between basic physic characteristics of reservoir VS. pressure have been established. Thus we can establish theoretical deliverability equations involving three kinds of well(vertical well, vertical well with vertical fractures and horizontal well) which are studied by using Darcy formula with consideration of mobility function, threshold pressure gradient, stress sensitivity and three-phase(oil, water and gas) flow. Edit a relevant software to calculate productivity sensitivity of low permeability wells and then make some analysis to oil wells in ChunLiang oil field. The conclusions are: the reasonable drawdown pressure upper limit is 36MPa; the model has a high accuracy in productivity calculation with a average relative error of 9.9%; when changing six parameters, to all the three kinds of wells, the reasonable drawdown pressure upper limit increases with stress-factor and water cut, decreases with solution gas-oil ratio; vertical well decreases with threshold pressure gradient while the other two keep still; when the horizontal length/fracture length change, there is totally no impact on inflection point; especially, to vertical well about threshold pressure gradient, 0.01 is an critical value, it is only sensitive while the value is greater than 0.01. Keep the same situation, let the horizontal length and vertical fracture length be 100 m, all the three kinds of well own the same inflection point which means that the reasonable drawdown pressure upper limit is not of great relevance in well types but in basic characteristic of rock and fluilds.