Drilling Of Gulf Of Suez Evaporites

Abstract

Abstract The Miocene evaporites of Gulf of Suez area comprise salt, anhydrite and, rarely, gypsum. They are mainly found south of 29 deg. N latitude line. Salt pillows and diapirs are common in the southern half pillows and diapirs are common in the southern half of Gulf of Suez and may be associated with upward salt creep. Hole enlargement, key seating, high pressure salt water flows, hole instability and drillability contrasts are some problems associated with the drilling of these evaporites. Careful preplanning taking into account in-situ behavior of evaporites, reduces the chances of developing any of the problems associated with their drilling. Introduction Since initial discovery of oil in Egypt, Gemsa field in 1910, extensive exploration has been carried out commencing with on shore drilling on both east and west coasts of the Gulf of Suez (GOS). Offshore exploration in the Gulf commenced in the early sixties and is still among the most active offshore areas of the Middle East. Gulf of Suez Petroleum Company (GUPCO) drilled its first offshore well in 1964 and to date more than 200 wells have been drilled including about 60 exploratory ventures. Total footage drilled by GUPCO exceeds two million feet and is increasing rapidly with 9 currently active rigs involved in exploration, workover and development drilling operations. The southern region of GOS has a very characteristic Miocene evaporite section which has a direct impact on well planning and drilling practices Many problems are encountered while drilling these evaporite sections. The object of this paper is to highlight the major problems pertaining to the specific mechanical and physical characteristics of the rocks comprising the Miocene Evaporites. This paper presents a brief discussion about the geology of the Miocene evaporites in the GOS area. Problems posed by hole enlargement, drillability Problems posed by hole enlargement, drillability variations and hole instability are discussed. Details are given regarding potential key seating and salt water flows. Also the repercussion of these problems in regard to casing and cementing program is problems in regard to casing and cementing program is summarized. An outline of a typical drilling program for these evaporites is contained in the program for these evaporites is contained in the appendix. GEOLOGY OF GOS EVAPORITES Miocene evaporites are very distinctive sediments of the GOS area. They comprise salt, anhydrite and, rarely, gypsum. The rock salt is mainly composed of sodium chloride. Evaporite thickness varies from 25 to in excess of 50% of the total Miocene and Post Miocene Sediments. Post Miocene Sediments. Miocene evaporites in the GOS are mainly found south of 29 deg. N latitude line and cover essentially all of the graben of Gulf of Suez. They occupy the whole southern part of the Gulf. Miocene evaporites have been recently found as far as the Sudanese border. Fig. 1 shows their location. Generally, the evaporite thickness increases towards the centre and south of GOS. Very rapid thinning occurs near 29 deg. N latitude. Conversely, a section in excess of 3050 meters (about 10,000 feet) of Miocene evaporites was encountered in Tawila Island Well No. 2.