Abstract:

In this study, based on Laplace transformation and Stehfest numerical algorithm, a vertical well fracture network reconstruction semi-analytical deliverability evaluation model which can be used for fractured tight oil reservoirs was established. The proposed model is a composite system with two concentric regions. The inner region contains finite number of hydraulic fractures and the flow in each fracture is assumed linear. The outer region is modeled with the classical WarrenRoot model and radial flow takes place in this region. The influences of related parameters, such as diffusivity coefficient ratio, fracture conductivity ratio, storativity ratio, cross-flow factor and so forth, on the seepage flow were analyzed by using the established model. The results show that the deliverability follows the “L” shaped decline law. Diffusivity coefficient ratio has effect on initial production. The bigger diffusivity coefficient ratio is, the higher initial production is. Fracture conductivity ratio has great impact on whole production cycle. Storativity ratio and cross-flow factor-influence degree and occurrence time of cross-flow respectively. When artificial fracture numbers or permeability is larger, coupled boundary flow is more obvious and productivity is higher, which shows that reconstruction volume and reconstruction degree both are important to deliverability, we also should pay attention to the reasonable optimization of both parameters. What’s more, two wells’ produce data were fitted, and some reasonable parameters were explained, which can prove the practicability of this model.

Key words: deliverability evaluation, fractured tight oil reservoir, fracture network reconstruction, composite system, Laplace transformation, Stehfest numerical algorithm