Pre-Drilling Production Forecasting of Parent and Child Wells Using a 2-Segment Decline Curve Analysis (DCA) Method Based on an Analytical Flow-Cell Model Scaled by a Single Type Well

Abstract

This paper advances a practical tool for production forecasting, using a 2-segment Decline Curve Analysis (DCA) method, based on an analytical flow-cell model for multi-stage fractured shale wells. The flow-cell model uses a type well and can forecast the production rate and estimated ultimate recovery (EUR) of newly planned wells, accounting for changes in completion design (fracture spacing, height, half-length), total well length, and well spacing. The basic equations for the flow-cell model have been derived in two earlier papers, the first one dedicated to well forecasts with fracture down-spacing, the second one to well performance forecasts when inter-well spacing changes (and for wells drilled at different times, to account for parent-child well interaction). The present paper provides a practical workflow, introduces correction parameters to account for acreage quality and fracture treatment quality. Further adjustments to the flow-cell model based 2-segment DCA method are made after history matching field data and numerical reservoir simulations, which indicate that terminal decline is not exponential (b = 0) but hyperbolic (with 0 < b< 1). The timing for the onset of boundary dominated flow was also better constrained, using inputs from a reservoir simulator. The new 2-segment DCA method is applied to real field data from the Eagle Ford Formation. Among the major insights of our analyses are: (1) fracture down-spacing does not increase the long-term EUR, and (2) fracture down-spacing of real wells does not result in the rate increases predicted by either the flow-cell model based 2-segment DCA (or its matching reservoir simulations) with the assumed perfect fractures in the down-spaced well models. Our conclusion is that real wells with down-spaced fracture clusters, involving up to 5000 perforations, are unlikely to develop successful hydraulic fractures from each cluster. The fracture treatment quality factor (TQF) or failure rate (1-TQF) can be estimated by comparing the actual well performance with the well forecast based on the ideal well model (albeit flow-cell model or reservoir model, both history-matched on the type curve).

Optimization of Fracture Spacing and Well Spacing in Utica Shale Play Using Fast Analytical Flow-Cell Model (FCM) Calibrated with Numerical Reservoir Simulator

“…What stands out from Figure 3a,b is that future wet gas wells, if completed with narrower cluster spacing, would have higher initial rates. Similar results were generated in earlier studies with flow-cell models (verified with CMG and KAPPA numerical simulators) for dry gas wells [12], and for black oil wells [9][10][11]. 1).…”

“…However, the wells with a narrower inter-well distance will suddenly start to decline faster (Figure 5b). The data point where the narrowly spaced wells leave the decline curve trend of the well with the largest inter-well spacing was coined the kick-off point [9,11]. For a given well spacing, there is only one kick-off point, which occurs at a given time in the life of the well, the so-called kick-off time.…”

“…The timing of the kick-off point occurrence in the well life (so-called kick-off time) follows from the depth of investigation formula for the diffusive pressure transient [16] and Figure 13 in Reference [11]. The depth of investigation (r i ) refers to the advance of the pressure draw-down front, which expands from the fracture tip outward.…”

“…The flow-cell model specifically aims to quickly generate physics-based DCA curves that can account for changes in the completion design parameters, as well as for variations in the well spacing. The model has been verified to forecast with high accuracy (>0.95) production rates and EURs of oil wells [9][10][11], as well as for dry gas wells [12]. The flow-cell model also circumvents time-consuming mathematical computations typical for fullblown reservoir simulators by focusing on the flow of hydrocarbons within a single cell in an existing well.…”

“…By assuming that all the flow cells within a well are identical, upscaling provides the flow rate of the well system, thus, providing a fast alternative for other analytical procedures, such as decline curve analysis, while preserving the physics-based nature of reservoir simulations. The spreadsheet-based FCM analysis was successfully tested against commercial reservoir simulators in a series of prior studies, focusing on black oil wells [9][10][11], then dry gas wells [12].…”