Seawater Project in Saudi Arabia - Early Experience of Plant Operation, Water Quality, and Effect on Injection Well Performance

Abstract

Introduction Large seawater supply development for water injection involves the application of technology in controlling chemically and mechanically interactive systems to achieve product quality, service reliability, and economy of size. Recent activities in Saudi Arabia to convert a large onshore subsurface saline water flood to treated seawater supply illustrates the magnitude of these problems and successful solutions achieved. This paper reviews early system experience. Plant Operations Plant Operations The treated seawater supply system is depicted in Fig. 1. Completely new facilities extend from the offshore intake and treating plant at Qurayyah to the suction of ‘Uthmaniyah Water Supply Station 1 (UWSS-1). Extensively revised, plus additional, pump trains are being provided at UWSS-1 and the five associated water-injection pump stations (WIPS).Operationally, principal problem areas occurred in fiberglass-reinforced piping (FRP) support and restraint and in sulfur dioxide (SO2) plant operation and metallurgy. These problems were resolved early in the plant operation. Water Quality The water quality standards for the seawater treatment plant were derived from either pilot studies or observation of other seawater flood projects. Table I gives the specification, measurement method, and origin.The water quality between Qurayyah and ‘Uthmaniyah showed considerable deterioration during the first 6 months. Several pigging operations and increased flow rates have cleaned the system so that present water quality meets specifications. present water quality meets specifications. Corrosion Corrosion of the treatment and distribution systems is a major concern in any water injection system. The following methods are used to monitor corrosion rates in the various parts of this system. Typical DataMonitor Method Qurayyah ‘Uthmaniyah Coupons and polarizationprobes, mil/yr 3 to 6 <2Iron, mg/L <0.01 0.01 to 0.02 At this time, system corrosion is well within acceptable limits. Early Performance of Injection Wells Seawater temperature varies from 15 to 38 deg. C, resulting in a viscosity range of 0.75 to 1.25 cp. Aquifer water temperature averaged 70 deg. C with a viscosity of 0.4 cp. This higher viscosity of seawater results in reduced injectivity. Preseawater Data Collection Preseawater Data Collection Model studies to evaluate the effects of lower water temperature indicated reductions in injectivity of up to 50% during the first 3 years of the project, with most of the decline occurring in the first month.Another major factor that could affect seawater injection performance is reservoir plugging arising from solids in the seawater.To provide base data from which to evaluate the extent of formation plugging, an extensive data collection program was undertaken. This program consisted of obtaining pressure falloff data on all injectors and continuous flow profile data on approximately two-thirds of the injectors. Average injectivity indices and skin factors were calculated. JPT P. 1709