Well testing interpretation for horizontal well with hydraulic fractures and interconnected micro-fractures

Abstract

As hydraulic fracturing technology has been widely used in practices, drilling a fractured horizontal well (FHW) is a common measure to improve the ultimate recovery of shale oil reservoirs. Many microseismic data show that multi-scale fracture networks can be generated along those FHW, including hydraulic fracture networks and natural fracture networks. The hydraulic fracture networks are comprised of hydraulic fractures (HF) and interconnected micro-fractures (IMF). To facilitate the productivity estimation, the first and primary work is to analyze the transient pressure responses of those wells. However, due to the complex geometries of HF and IMF, analyzing the pressure responses of those FHW is challenging. Thus, lots of work need to be done.In this paper, a well testing model of FHW is developed with the hydraulic fracture networks and natural fracture networks using a semi-analytical approach. The semi-analytical approach is presented by discretizing both HF and IMF into fracture segments. The Laplace transformation, source function, and superposition principle are used to solve the well testing model. With model solutions, we can obtain the pressure response of the FHW. Then, a numerical verification is presented to verify the reliability of the proposed model. Sensitivity analysis is also conducted to study the impacts of different parameters on the pressure responses. Finally, we use this model to perform a type-curve matching and evaluate the stimulation effectiveness on an actual well from the Jimusar Sag.The results show that pressure response of a FHW with complex fracture networks can be divided into six flow regimes, including: (1) first bilinear flow, (2) “IMF-HF” support, (3) second bilinear flow, (4) formation linear flow, (5) crossflow from matrix to natural fracture networks, and (6) pseudo radial flow. Sensitivity analysis shows that with the increase of HF number, HF length, or HF conductivity, the phenomenon of “IMF-HF” support becomes weaker. With the increase of the IMF number, IMF length, or IMF conductivity, the phenomenon of “IMF-HF” support becomes stronger. Different flow regimes have different features, which provides a good guideline for parameter estimation of fracture networks.