Challenges and Achievements of Drilling Maximum Reservoir Contact (MRC) Wells in Shaybah Field

Abstract

Abstract Saudi Aramco's drilling strategy witnessed a change in year 2002 from drilling horizontal wells to more challenging and extended reach maximum reservoir contact (MRC) wells in Shaybah field. The objectives behind this change were to achieve the following: Improve the well productivity by providing maximum reservoir contact, reduce the unit cost of drilling ($/ft) and production ($/bbl), and to utilize the limited space more efficiently in the Sabkhah (flat areas between huge sand dunes). Different types of MRC wells were drilled, such as fork and fishbone in both open hole and cased hole to allow installing of intelligent completion packers for controlling the rate of production from each lateral. The reason for drilling different types of wells is to evaluate the impact of a well's type on the performance of the reservoir. The longest reservoir exposure ever drilled in Saudi Aramco was achieved by combining between the fork and fishbone in one well reaching up to 12.3 km (7.6 miles). Up to April 2003, eight MRC wells of different types and with 67.4 km (41.9 miles) of reservoir exposure were drilled in Shaybah field. Introduction Field History The Shaybah field, discovered in 1968, in the Rub'al-Khali desert of Saudi Arabia, is approximately 13 km (8 miles) wide and 64 km (40 miles) long. The surface terrain is comprised of salt flat areas known as sabkhah and mountainous sand dunes (up to 200 meters high). Because of its rugged character, the field is developed from flat sabkhas necessitating highly accurate directional drilling to reach the targets. The oil in the Shu'aiba formation is Arabian Extra Light with an average API of 42° and a solution GOR (Gas-Oil-Ratio) of 750 SCF/STB. It was developed in the mid 1990s using one-km horizontal wells (single-lateral) targeting the Shu'aiba reservoir. The presence of a large overlying gas cap and a relatively weak aquifer dictated the use of horizontal completion to minimize the potential for early gas breakthrough while achieving economically-desirable production rates. The field went into production in July 19981. Definition MRC wells are defined as having an aggregate reservoir contact in excess of 5 km through a single or multi-lateral configuration1 Objectives: The year 2002 represented a quantum leap for Saudi Aramco's drilling strategy in the Shaybah field. MRC wells were required in areas with low permeability in order to minimize the drawdown and to maximize the sweep efficiency. This drastic change extended to both well types and reservoir contact extent. Employing the available technology and preparing the wells to accommodate future development in the oil industry were taken into consideration. The major objectives of this strategy are to achieve the following:Improve the well productivity by providing maximum reservoir contact.Reduce the number of wells and the surface facilities to put these wells in production.Reduce the unit cost of drilling ($/ft) and production ($/bbl).Utilize the limited space in the Sabkhah more efficiently. Field History: The Shaybah field, discovered in 1968, in the Rub'al-Khali desert of Saudi Arabia, is approximately 13 km (8 miles) wide and 64 km (40 miles) long. The surface terrain is comprised of salt flat areas known as sabkhah and mountainous sand dunes (up to 200 meters high). Because of its rugged character, the field is developed from flat sabkhas necessitating highly accurate directional drilling to reach the targets. The oil in the Shu'aiba formation is Arabian Extra Light with an average API of 42° and a solution GOR (Gas-Oil-Ratio) of 750 SCF/STB. It was developed in the mid 1990s using one-km horizontal wells (single-lateral) targeting the Shu'aiba reservoir. The presence of a large overlying gas cap and a relatively weak aquifer dictated the use of horizontal completion to minimize the potential for early gas breakthrough while achieving economically-desirable production rates. The field went into production in July 19981.