The Development of the Ardeshir Field

Abstract

This paper describes the successful development of the Ardeshir Field offshore Iran, using an unconventional approach. Development centered on the use of two slant-mast, self-contained drilling rigs designed especially for this field. Sixty-six wells were completed using these slant rigs. Introduction Iran Pan American Oil Co. (IPAC) is a joint venture company formed by National Iranian Oil Co. and Amoco International Oil Co. on an equal partnership basis. IPAC operates four producing oil fields offshore Iran (Fig. 1).The Ardeshir Field (one of the four Amoco-operated fields) is located in 120 ft (36.6 m) water offshore Iran about 45 miles (72.42 km) west of Kharg Island. The field was declared commercial. In Dec, 1970, after drilling six mudline suspension, delineation wells. This paper describes the successful development of this large paper describes the successful development of this large unique reservoir, which required an unconventional approach. The structure is about 15 miles (24 km) long × 5 miles (8 km) wide, with a maximum oil column thickness of 150 ft (45.7 m). A moderately viscous sour crude oil [14 cp (3.4 mPa)] of 27 degrees API (0.9 g/cm) gravity is produced from the Ghar formation, an unconsolidated sand of Lower Miocene age.Core permeability of the Ghar sand averages 2.5 darcies, with porosities of about 30%. The oil zone is overlain by an initial gas cap with a 60-ft (18.3-m) gas column at the crest and underlain by an aquifer expected to be active and large in areal extent.Full-scale field development began in early 1976 with production starting in Nov. 1976. In Dec. 1978 the field production starting in Nov. 1976. In Dec. 1978 the field achieved our production objective rate of 200,000 BOPD (31 797 M /d oil) on a sustained basis from 61 active producers. Subsequently, one of the two slant-mast rigs producers. Subsequently, one of the two slant-mast rigs was released, and the remaining rig used for continued development drilling and workovers.Because of the relatively shallow depth of the producing formation, unusual techniques were employed producing formation, unusual techniques were employed to develop the field, The development program centered on the use of two slant-mast, self-contained drilling rigs that were designed specifically to operate from 28-slot, fixed platforms. Each platform had 10 vertical, eight 20 degrees, two 25 degrees. and eight 30 degrees conductors. The slant conductor concept was used to maximize the departure of the directionally drilled wells and thereby increase the drainage area of each platform. Sixty-six wells were completed using these slant rigs on the four 28-slot platforms installed. An additional nonloadbearing platforms installed. An additional nonloadbearing platform with nine vertical slots also was installed that will platform with nine vertical slots also was installed that will use a conventional jackup rig for drilling. Eventually, up to 10 platforms may be installed in the Ardeshir Field. Geology The Ardeshir Field produces hydrocarbons from an Oligo-Miocene age reservoir called the Ghar sandstone formation, which occurs 2,800 ft (853 m) subsea. This unit can be divided into three members:a basal carbonate called the Asmari,a middle member called the Ghar sandstone, andan upper carbonate-anhydrite unit called the Lower Fars pay. JPT P. 821