Cost Saving Through Wax and Scale Management Strategy in Offshore Marginal Field, Malaysia

Abstract

Abstract One of the offshore marginal oilfields in Malaysia has been suffering from a combination of downhole wax and scale deposition. In order to address the issue, a wax and scale management strategy has been developed with the objectives of sustaining optimum production with minimum expenditure spent on repetitive remedial activities due to wax and scale deposition downhole. Pour point of the crude oil has been measured and the temperature profiles in the wells have been modelled. The result indicates that there is potential for wax deposition downhole. The formation water analysis from major reservoirs has been used as input for scaling model. The output shows scaling tendency ranging from moderate to high. Learnings from Scale Inhibitor Squeeze Treatment (SISQ) pilot recommend that the wax and scale need to be removed from the tubing before commencing the inhibition. Wax dissolver and acid bullheading treatments were also trialed in some wells, yielding positive result. Based on various treatments carried out in the past, this paper details the wax and scale removal actions, preventive measures to inhibit new deposition, and key parameters to monitor with monitoring frequencies as part of post-inhibition surveillance strategy. Crude oil analysis from the major reservoirs confirms downhole wax deposition potential. With the pour point of 45 degrees Celcius (°C), the crude has high tendency to gel up downhole since the wells are cooled when gaslifted. Some of the completion strings are equipped with chemical injection valves for wax inhibition while others have only the gaslift valves. The paper recommends the wax inhibition chemical to be injected downhole through either chemical injection valve or into the lift gas stream so that the crude can be treated when the temperature is still above the pour point temperature. Based on the deposits analyses, the scale found in the production tubing is CaCO3. SISQ technique has been considered as to provide scale inhibition right at the reservoir while acid bullheading technique provides fit-for-purpose scale removal action down to sandface completion. The management strategy starts by removing the existing deposition in the tubing by means of wax and scale dissolver chemical bullheading supplemented by tubing gauge cutter run campaign, followed by the continuous injection of pour point depression and wax inhibitor through the chemical injection valve or lift gas stream for the low temperature wells. The monitoring program includes produced water chemistry composition comparison with baseline, the concentration of scale inhibitor returned compared with minimum inhibitor concentration, pour point temperature, wax appearance temperature (WAT), wax inhibitor dosage for further optimisation, and quarterly slickline gauge run. Finding from gauge run will determine the chemical effectiveness and also serve to clear the tubing from any possible deposits. Historically, remedial solutions were carried out by means of repetitive coiled tubing and chemical bullheading jobs. Wax and scale build-up in the tubing costs not only production deferment, but also expensive jobs to restore the production. With the management strategy established, the field is expected to save around RM 96 million from recurring remedial operations and avoidance of an estimated 121k bbls production deferment due to wax and scale over the remaining field life.