Utilizing Surface Parameters in Determining Periodic Chemical Injection Treatment Intervals for Aged Water Disposal Wells

Abstract

Following the last couple of years marked by a drop-in oil price, there has been a requirement to optimize costs for operating and maintaining existing and ageing facilities and equipment and Water disposal wells are no exception. Case study considered onshore wells which were initially completed as oil producing wells in the mid-1970s to early 1980s and in their later life converted for water disposal after the Ultimate Recovery (UR) of the associated reservoirs had been reached and produced water injectivity for wells positively ascertained. The need to initiate this method of produced water management was to ensure its proper and efficient disposal in line with best practices, government regulations and associated cost efficiencies. As these wells stay long in service, they witness several impairments that affect their injectivity. These impairments amongst others include oil slippages, suspended solids, fine sand, corrosion products, microbial activity and carbonate scale particles. These in turn create blockage around perforations which reduce the effective path area for movement of water molecules into subject reservoirs. One of the key actions in maintaining ‘old’ water injection wells is periodic chemical treatment to ensure optimal injectivity. Chemical treatments maybe conducted routinely as a preventive and corrective maintenance activity. As a view to optimising costs we looked to change this to a "Just-in-time" treatment philosophy to manage its overall impact on operating costs and schedule for execution. A surveillance program was developed for older water injection wells which do not have sophisticated sub surface gauges, by relying on surface parameters and associated equipment condition monitoring to schedule chemical treatments for the water injection wells. Some of the surface parameters that was utilized are Water Injection Pump Discharge Pressures, Injection Tubing Head Pressure (ITHP), Injection Flow Line Pressure (IFLP). Following analysis, an empirical system has been developed that enables the prediction for chemical injection treatment without the need to conduct sub-surface investigations using Coil Tubing equipment. This paper discusses a simple, cost effective and easy to use methodology which can be adopted as a first step towards ensuring the adequacy of water injection surveillance program.