Novel Solutions for Transient Sandface Temperature in Dry-Gas-Producing Wells
Authors: Carpenter Chris 
Published: March 2017

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 181057, “Novel Solutions and Interpretation Methods for Transient Sandface Temperature in Vertical Dry-Gas-Producing Wells,” by Akindolu O. Dada, Khafiz M. Muradov, and David R. Davies, Heriot-Watt University, prepared for the 2016 SPE Intelligent Energy International Conference and Exhibition, Aberdeen, 6–8 September. The paper has not been peer reviewed.

The application of high-precision downhole temperature sensors has resulted in pressure-transient analysis (PTA) being complemented or replaced by temperature-transient analysis (TTA). However, the derivation and use of TTA solutions is challenging because of the small value of the measured temperature change and the more-complex nature of the governing physics and equations. In particular, analysis work flows for wells producing gas or gas/liquid mixtures are still lacking because most published liquid TTA solutions cannot be applied in the presence of gas. The complete paper addresses a work flow for a dry-gas-producing well.

Introduction

Applications of downhole temperature measurements can be divided into two broad classes based on the type of temperature models used and the reservoir-flow regimes analyzed. The first class uses semisteady-state models, usually in conjunction with measurements made at a single point in time by distributed-temperature sensors (DTSs). The second class of models uses TTA with both point and distributed measurements made over a period of time.

TTA is relatively tolerant to measurement accuracy. It essentially requires data on the rate of temperature change, which is normally measured one or two orders of magnitude better than the absolute values (i.e., the difference between the sensor’s resolution and the sensor accuracy).

The combination of TTA and PTA potentially allows the comprehensive estimation of zonal reservoir properties and flow rates from a single transient event. However, this will be realized only when a comprehensive set of TTA solutions is available for the heat- and mass-transfer models in porous media required to cover all the downhole scenarios frequently encountered during well production.

Most of the work performed in the area of transient-sandface-temperature modeling has been limited to slightly compressible fluids (liquids), a limitation that allowed the introduction of simplifying assumptions to the thermal models. In contrast, the essential step of extending TTA to compressible fluids (gases) results in a highly nonlinear mathematical problem that is more difficult to solve.

The complete paper develops analytical models for predicting transient sand-face temperature in gas-producing wells and illustrates their use for reservoir monitoring and flow-rate allocation. As such, it represents a major contribution to the development of a comprehensive TTA work flow.

Underlying Physical Processes

Full details of all equations, assumptions, derivations, and work flows regarding related phenomena are provided in the complete paper.