Impact of Thermal Interference in an Offshore HPHT Gas Field Development

Abstract

Abstract Field-X is a large greenfield high pressure high temperature (HPHT) carbonate development located off the coast of Sarawak, offshore Malaysia. The current development plan requires each of the wellhead platforms (WHP) to have multiple high-rate gas wells to meet the Daily Contract Quality (DCQ) requirements. When closely spaced wells produce simultaneously, they can perturb the local geothermal temperature profile, and affect the thermal response of individual wells. This can also impact the platform pile and conductor strengths, and infill well designs. This paper outlines a technique to evaluate formation temperature shifts when closely spaced wells are produced concurrently and apply that to validate the design basis for the new development. The approach used here is based on an integral formulation of the heat conduction equation, employing Green’s functions and a fast numerical solution method. Prior to thermal interference, a wellbore is considered a flux-limited (Neumann) source, while post-interference, it functions as a constant temperature (Dirichlet) heat source. This method calculates the time needed for interference among wells arranged in a grid layout and determines the temperature at any point in the formation over time. For computational reasons, commercial wellbore simulators assume a far field boundary at a distance 10 – 15 wellbore radii from the axis. All points outside this boundary are assumed to remain at the undisturbed temperature. This assumption must be relaxed to when there is thermal interference. Traditionally, finite element methods have been used for these calculations. This paper demonstrates a semi-analytical method that is simpler to develop and does not require additional software or hardware. The method can be used for other fields with similar nature of wells.