Downhole Scales Associated with October Field Formation Waters and Water Injection Using a Shallow Aquifer

Abstract

Abstract Gulf of Suez Petroleum Company (GUPCO) has been producing from October field since 1977. Currently the total daily production from the field is 80 MBFPD with average water cut 76 %. October field contains four formations with extremely different characteristics. Each formation has unique combination of lithology, downhole conditions, and formation water chemistry. Through the whole life of October field, more than 300 downhole scale samples were collected, in addition to more than 180 wellhead water samples were completely analyzed. This set of data can be used to categorize formations according to their capability to deposit a certain type of inorganic scale. After reservoir depletion, sea water had been used in water injection. By the time, field needs changed and a shallow water aquifer replaced sea water in supporting some reservoirs. Several compatibility tests and scale tendency calculations had been done before using the shallow aquifer (Zeit formation). Each well was experiencing different production conditions which dedicated deposition of certain types and amounts of inorganic scale. Scale deposition depth depended on the degree of mixing between incompatible waters, and the introducion of pressure or temperature changes along wellbore. After water breakthrough, some pressure-supported wells faced some carbonate scale deposition due to the dissolved carbon dioxide in Zeit water. Generally, Zeit formation can be used as a good alternative for sea water in water injection projects in Gulf of Suez area. Some formations contain a self-scaling water which has the ability to deposit sulfate and sulfide scales without mixing with any other water e.g. Nubia formation water. Sea water cooling, in offshore wells, usually forces scale deposition at shallow depths especially against the downhole safety valve and Christmas tree valves. This study is expected to be a good tool in recommending scale inhibition methods or products for new wells drilled in October field or any analogous field. This study can compensate for the gap between commercial scale prediction software and actual scale deposits, as most current software products rely only on thermodynamic equations for surface-collected water samples.