Pressure-Transient Analysis to Diagnose the Inefficiency Production Locations of Hydraulic Fractures in Highly Deviated Wells
Authors: Bai Wenpeng , Cheng Shiqing , Xu Zexuan , Guo Qiao , Wang Yang 
Published: September 2023

ABSTRACT
Formation heterogeneity and differences in fracture closure degree result in varying contributions of different fractures to the total oil production. This paper considers the effect of unequal oil production rates of each fracture on pressure-transient behaviors and develops a semi-analytical model to diagnose inefficiency production locations of hydraulic fractures in highly deviated wells using bottomhole-pressure data. Firstly, new semi-analytical solutions of a multi-stage fractured highly deviated well are derived based on the Green function and Newman product method. Secondly, the model is validated through comparison with a numerical model in KAPPA software. Thirdly, type curves are developed, and sensitivity analysis is further investigated. The results show that early radial flow is distinguishable and behaves as a horizontal line with a value of 0.5/N* (N* is the actual number of fractures) in the pressure-derivative curves. Finally, a case study is conducted in the Xinjiang oilfield, indicating the feasibility of the proposed model in analyzing formation parameters and diagnosing inefficiency production locations of fractures.

INTRODUCTION
Hydraulic fracturing has become a widely used technology to enhance oil and gas production from low-permeability reservoirs (Sun et al., 2015; Wang et al., 2020; Wei et al., 2022a). However, the interpretation of pressure data from hydraulically fractured wells is challenging due to the complex nature of hydraulic fractures and their interactions with the reservoir (Zerzar and Bettam, 2004; Bettam et al., 2005). Additionally, highly deviated wells pose additional challenges to the interpretation of pressure data, as the pressure and flow behavior can be significantly different from vertical wells. Giger (1987) first studied the seepage field and pressure distribution of fractured horizontal wells. In the 1990s, many scholars studied the unstable pressure characteristics of fractured horizontal wells produced under the conditions of infinite conductivity and finite conductivity vertical fractures (Kuchuk and Habusky, 1994). Al Rbeawi and Tiab (2012) proposed a pressure transient analysis method for horizontal wells with multiple inclined hydraulic fractures using type-curve matching. Cinco (1975) proposed the transient pressure solution of the inclined well and analyzed the influence of the deviation angle on the pressure derivative curve. Cinco (1981) proposed the pressure transient analysis method for vertical fracture with finite-conductivity fractures. Pressure transient analysis become an undeniable demand for evaluating well performance and reservoir characteristics (Cinco et al., 1978; Abbaszadeh et al., 1990; Khatteb et al., 1991; Ozkan et al., 2000). Some scholars have made a lot of contributions to the pressure transient analysis of multi-stage fractured horizontal wells (Zerzar et al., 2004; Medeiros et al., 2010; Ozkan et al., 2010; Wang et al., 2021; Wei et al., 2022b). In highly deviated wells, pressure-transient analysis can be particularly useful in identifying inefficient production locations of hydraulic fractures. Unequal oil production rates from each fracture can result from formation heterogeneity and the difference in fracture closure degree, and this can significantly impact the pressure behavior observed in the wellbore (Qin et al., 2018; He et al., 2016). This paper presents a method using pressure-transient analysis to identify inefficient production locations of hydraulic fractures in highly deviated wells. A semi-analytical model is developed to consider unequal oil production rates and validated with numerical simulations. Type curves are developed for sensitivity analysis. A case study in the Xinjiang oilfield demonstrates effectiveness in analyzing formation parameters and diagnosing inefficiency production locations of fractures.