Water Treatment And Injection System In UMM Shaif Field Offshore Abu Dhabi
Authors: Ayad N.A. , El-Hadidi S.M. 
Published: December 2007

The water treatment and injection system used by Abu Dhabi Marine Operating Company in UMM SHAIF FIELD is designed for a total normal capacity of 700,000 BWPD of treated seawater at a nominal pressure of 1500 psig. The system consists of seven identical modules, each with a maximum design capacity of 100,000 BWPD of treated sea water having a turbidity of less than 0.2 FTU (Formazine Turbidity Unit) and containing less than 10 per cent of 2–10 micron particles contained in the raw seawater.

Each water injection module consists of two winning pumps, four deep up-flow pressure sand filters, two-stage vacuum tower, booster pump and two high pressure injection pumps. Facilities are provided to inject chemicals such as Chlorine, Bentonite, Cationic Polyertrolyte, Oxygen Scavenger, Scale inhibitor and Organic Biocide. Treated water from the modules is distributed to the injection wells by a number of 14 and 24 inch submarine lines cross-connected at the riser platform to permit balancing of flows between lines. Operational adjustment to the plant can only be performed from control panels local to the modules. performed from control panels local to the modules. The modules are designed for continuous unattended operation.

In order to control the quality of water injected, various tests are carried out on routine basis at selected sampling points at the platform and at the wellheads. These tests measure suspended solids, turbidity, dissolved oxygen, free chlorine sulphides as H2S, bacterial population, total and dissolved iron, as well as corrosion rates.

Due to favourable environmental sea conditions of temperature and water composition, sulphate reducing bacteria are available in abundance in raw seawater. SRB reduces sulphate ions in the water and gives rise to H2S as a corrosive by-product. The control of this type of bacteria and limitation of their activities and growth is of great importance. ADMA-OPCO experience in this regard is presented in this paper. presented in this paper. The water injected in Power injection wells is of adequate quality. This is demonstrated by the volume of water collected through double 47 mm - 0.45 millipore filter at the wellhead sampling point and the stable injectivity indices experienced for powered injection wells.

Introduction

The Umm Shaif Arab 'D' reservoir is a massive hydrocarbon accumulation located offshore, some 160 kilometers North-West of Abu Dhabi in the United Arab Emirates (Figure 1). It is a dome like structure overlaying a deep salt plug. The dome has gentle dip (2 - 3 deg.). The structure is of approximately 18 kilometers by 24 at the furthest Arab 'D' oil water contact. Initial in-place values for this saturated oil reservoir were 9.97 billion STBO and 15.79 trillion SCF of free gas. Presently, the production from Arab 'D' reservoir Presently, the production from Arab 'D' reservoir averages 250,000 STBD of oil.

The reservoir was produced by primary depletion from 1962 until 1974 when a dumpflood scheme was initiated. Conversion of dumpflood injectors to power injectors started in 1976. Presently, there are 14 power injection wells Presently, there are 14 power injection wells and 11 dumpflood wells (Figure 2). All the dumpflood wells will be converted to power injection to provide full pressure maintenance in the reservoir. A replacement factor of 1.8 BW/STBO is adequate to maintain the pressure at all points in the reservoir above the local bubble points in the reservoir above the local bubble point pressure. When significant water production point pressure. When significant water production is encountered, a larger injection/production ratio is required. A build-up of water injection capacity is shown in figure 3.

The water to be injected in Arab 'D' reservoir should be of good quality.