Method of calculating productivity of vertical wells with horizontal fracture in five-spot well pattern in low-permeability reservoirs

Low-permeability oil layers with poor physical properties and oil-bearing performance become the main potential reservoir when multilayer reservoir enters the stage of ultra-high water cut. Shallow low-permeability reservoirs may develop horizontal fractures after artificial fracturing, so the effect of threshold pressure gradient should be considered. For this purpose, analysis was conducted to the seepage field characteristics induced by elliptical horizontal fractures in five-spot well pattern, and the calculation formula of the productivity of oil and watr was inferred by pressure loss caused by comprehensively threshold pressure gradient, material balance relation inside the reservoir as well as pressure drop superposition principle. Non-water flooding independent untabulated reservoirs in Xingshugang oilfield of Changyuan is taken as a practical case. Its dynamic indicators like oil production, water cut and recovery rate with five-spot well pattern fracturing are calculated and analyzed during the water flooding development process by using the productivity formula. It is found that injector-producer spacing, fracture dimensionless flow conductivity and initial oil saturation had an obvious effect on fracturing water-flooding productivity. And the average oil production of single well had a sharp decline after being put into production; even though expanding well spacing retarded the decline, the recovery percent dropped obviously. The main producing stage in this block was the period of strong water flooding (water cut 60%), and the percentage of produced geological reserves was higher when the initial oil saturation was lower.