Permanent Caprock Abandonment P&A Assessment Incorporating Rock Mechanics Analysis: Petrophysics Perspective

Abstract

Well abandonment has been associated and considered since in the Field Development Plan stage. Worldwide, government and legislative authorities are having specific requirement and regulation in ensuring the oil and gas industry to seal and permanently take offline unproductive wells to prevent them from impacting the environment and safety. When all feasible opportunity is exhausted and no remaining economic potential is proven in a well or field, it will proceed to abandonment, saving money spent on well liability cost. In effort to reduce the P&A cost which has no financial return, operators and regulators strive to improve P&A method to increase efficiency without compromising safety. The production of oil and gas, whether or not enhanced by the injection of water or gas, will cause a change of pressure, stress and temperature in the reservoir and its surrounding formations. Additionally, chemical characteristics of the injectant, may reactive gases for storage or production enhancement, may lead to changes in petrophysical, geomechanical and chemical properties of subsurface formations, faults and wells equipment. These changes may or may not have a detrimental effect on the containment of toxic or otherwise harmful fluids and gasses in the subsurface. The comprehensive P&A analysis and program is vital to ensure the security of well containment. Loss of containment may lead to potential loss of life, assets, environment and reputation. This paper will discuss the analysis done by Petrophysicist in supporting the decision and design of well P&A design, either isolation at reservoir level or caprock level. After no remaining potential and shallow hydrocarbon is verified, the well will be conditioned for pressure analysis and caprock assessment, by formulating well dynamic strength parameters, namely Young modulus and UCS and establishing pressure column. The competent caprock at the proposed barrier depth will be assessed, benchmarked and inventoried for regional caprock understanding, taking account input from multidiscipline. In addition to additional assessment on rock strength in well P&A design, this paper also recommend the multidiscipline future collaboration assessment technique for better regional caprock understanding. When possible, this method is able to provide feasible P&A design with some confidence level at the competency of the withholding caprock.