Permeability Enhancement of Conventional Geothermal Wells

Abstract

All geothermal systems require some degree of permeability to create heat convection and allow transport of this heat from below the earth to the surface. Production and injection capacities depend largely on this permeability hence, a poor or low permeability is a perennial concern of geothermal operators even in highly convective systems.

A review of the existing stimulation techniques to improve wellbore permeability, i.e. hydraulic fracturing and acidizing have shown that specific frac programs and acid treatment can be designed to match specific rock types, formations and pressure/temperature conditions with favorable results. Published reports of numerical and analytical simulations, as well as laboratory experiments indicated that permeability of fractures responds differently to changes in confining pressures, shear displacements and fluid-rock interactions. The current study will focus on hydraulic fracturing to investigate results obtained from actual field data where production or injection capacity of wells had been substantially increased (>>100%) with continuous injection of fresh water, cooling tower condensates or waste brine. To achieve this, core samples and drilling cuttings, preferably taken from these wells, will be subjected to a fluid-rock interaction in a flow-through simulator to characterize the specific chemical reactions that will occur, and will be tested in a laboratory pressure vessel to measure permeability and examine its behavior vis-à-vis changes in fluid flow, confining pressure and temperature. Ultimately, the end result is expected to generate an effective site specific hydraulic fracturing program, and hopefully produce practicable correlations to predict results.

Presently, this paper summarizes the results of the review, and outlines the works to be done necessary to accomplish the objectives of the current study.