Temperature-Prediction Model for a Horizontal Well With Multiple Fractures in a Shale Reservoir
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SummaryDownhole temperature measurements, either by permanent sensors or temporarily conveyed tools, provide information that has been used in many production-diagnosis applications. This paper presents a study that correlates the temperature behavior to the flow profile in a multistage-fractured horizontal well. The ultimate goal is to interpret well performance and to optimize fracture-treatment design from monitored temperature data.This study has developed flow and thermal models for a system of horizontal wells with transverse fractures under single-phase gas-flow conditions. The system was divided into a horizontal wellbore and a reservoir having multiple fractures. The wellbore-flow and -thermal models were formulated on the basis of mass, momentum, and energy balance. Numerical reservoir simulation was adopted for the reservoir-flow problem, and the reservoir-thermal model was formulated by a transient energy-balance equation, considering viscous dissipation heating and temperature variation caused by fluid expansion in addition to heat conduction and convection. In the reservoir system, the primary hydraulic fractures perpendicular to the horizontal well were modeled explicitly with thin grid cells, and the fracture network around the horizontal well was modeled as an enhanced-permeability zone with respect to the unstimulated-matrix permeability. The reservoir grids between two fractures were spaced logarithmically to capture transient-flow behavior. The reservoir-flow and -thermal models were coupled with the wellbore models to predict the temperature distribution in a horizontal wellbore. The results of the models show two main mechanisms in this thermal problem: head conduction by formation heating/cooling effects at nonperforated zones and wellbore-fluid mixing effects, with reservoir inflow at fracture locations (fluid-entry points).The examples in the paper illustrate that the models can be used to predict temperature profiles in stimulated horizontal wells for identical or nonidentical transverse fractures. Sensitivity studies were performed to evaluate the influences of fracture conductivity and half-length on temperature behavior in the defined system. The results indicate that the wellbore temperature is sensitive to both the fracture geometry (fracture half-length) and the conductivity across the investigated data range, though they showed different behaviors with time. This work shows that realtime post-fracture temperature-data measurement offers the potential to help evaluate created-fracture parameters, such as fracture conductivity and effective half-lengths.
