Abstract

Rate transient analysis (RTA) is an important method to predict productivity and reserves for reservoir and completion characterization in unconventional plays. In addition, multi-horizontal-well pads are a common development method for unconventionals. Close well spacing between multi-fractured horizontal wells (MFHWs) in multi-well pads results in significant interference from adjacent MFHWs. For RTA of production data from multi-horizontal-well pads, the influence of adjacent MFHWs cannot be ignored. In this work, we propose a semi-analytic RTA model for the multi-horizontal-well pad with arbitrary multiple MFHWs properties and starting production times. Combining Laplace transformation and finite difference analysis, we obtained a general solution of a multi-well mathematical model to use in RTA. Our model is applicable to cases of multiple MFHWs with different bottom hole pressures (BHP), varying hydraulic fracture properties, and different starting production times. In the solutions, we observe bilinear flow, linear flow, transition flow, and multi-MFHW flow. Rate normalized pressure (RNP) and its derivative are also affected by multi-MFHW flow. Two case studies revealed that the negative effect of interwell interference on the parent well productivity is closely related to the pressure distribution caused by the production of child wells.

Introduction

RTA allows us to predict oil and gas well production rates and reserves to characterize formations and effectiveness of completions. (Lee and Wattenbarger 1997). RTA requires only production data (rate and pressure) and does not require long-term shut-in for pressure build up tests, and as such, most research has focused on RTA in unconventional applications (Lawal et al. 2013; Sahai et al. 2015; Yadav and Motealleh 2017; Ravikumar and Lee 2019; Baek et al. 2019; Yuan et al. 2019; Chu et al. 2019b). Development of unconventional resources relies on horizontal drilling and multi-stage fracturing (Chun et al.2020). Infill drilling is also common. Operating companies usually prefer to concentrate drilling rigs to core areas. For example, Fig. 1 shows the distribution density of horizontal wells in Mountrail County, ND, and indicates that the well spacing among multiple MFHWs in the same horizon was as small as 660 ft (Krishnamurthy et al. 2019). For production data analysis of MFHWs in this kind of multi-well pad, interwell interference and connectivity have become realistic issues that must be considered (Anderson et al. 2016).

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