Evaluation Methods for Suspended Solids and Produced Water as an Aid in Determining Effectiveness of Scale Control Both Downhole and Topside

Abstract

Abstract The formation of mineral scale (carbonate/sulphate/sulphide) within the near well bore; production tubing and topside process equipment has presented a challenge to the oil and gas industry for over 50 years. Chemical methods to control scale have been developed including scale squeeze treatments and continual chemical injection. A key factor to the success of such treatment is the understanding of chemical placement and the effectiveness of the treatment chemicals. Evaluation of residual chemical concentration or scaling ion chemistry has long been used in monitoring programs and more recently probes have been developed which increase the rate of evaluation/interpretation. All these methods prove that the chemical is present in the brine when sampled or that scale formation is not occurring at the point of brine analysis. Evaluation of suspended solids in terms of amount, mineral type, composition and texture has been used along with brine chemistry to improve our understanding of the location of scale formation within production environments. This paper outlines the experimental methods developed and will site examples from the North Sea of the use of suspended solids analysis by environmental scanning electron microscope (ESEM) and the associated brine chemistry to evaluate the scale risk within the produced brine. The combination of these methods has improved integrated scale management in terms of evaluating scale squeeze placement effectiveness, squeeze lifetime and topside scale control challenges vs. separation problems. The publication of this method with clear examples of the value it can bring to an integrated scale management program for a field throughout its life cycle will benefit both emerging deep water (evaluation of placement) and more established oilfield operations (reducing chemical costs). Introduction The development of subsea facilities many with horizontal production wells to improve the economics of marginal oilfield developments has focused attention on the need to monitor the performance of scale control program applied both downhole and to flowline. The following short section outlines some of the monitoring methods currently used to date that can assist in the development of a continuous improvement loop part of an integrated scale management program. An example of such a management program is presented in Figure 1. Scale Inhibitor Monitoring Methods Scale inhibitor performance monitoring. Historically the methods of monitoring the performance of a scale inhibitor program have relied on analysis of chemical residual and scaling ion concentration. More recently the development of real time monitoring has taken the management of such programs to a new level. Results are presented in the following sections that show that an understanding of the types of scale present, their textures within produced fluid via ESEM adds an extra dimension to the understanding of scale management for downhole and topside applications. A knowledge of the performance of the inhibitor in laboratory tests has historically been used to determine whether or not a particular system is protected1. This requires confidence in the correlation between laboratory results and field application. If the amount of scale inhibitor present is above the laboratory established Minimum Inhibitor Concentration (MIC) then the system is considered protected.