低渗油层五点井网水平裂缝直井产能计算方法

多层油藏进入特高含水阶段以后，物性、含油性差的低渗油层成为主要挖潜对象，埋深浅的低渗油层人工压裂后容易形成水平裂缝，并且需要考虑启动压力梯度的影响。为此，分析了五点井网中椭圆水平裂缝诱发的渗流场的特点，综合启动压力梯度造成的压力损失、储层内的物质平衡关系以及压降叠加原理推导得到油水两相的产能计算公式。以长垣杏树岗油田未水洗的独立型表外储层为例，利用产能公式计算分析了五点井网压裂后水驱开发过程中的产油量、含水率以及采出程度等动态指标。研究发现:注采井距、裂缝无因次导流能力和初始含油饱和度对压裂水驱开发的产能影响很大；投产后平均单井产油量递减速度很快，扩大井距虽有助于减缓递减但明显降低了采出程度；区块主要的采出阶段是在较强/ 强水淹（含水率大于60%）时期，并且初始含油饱和度越小，这一时期采出的地质储量占比越大。

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.