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Abstract
The paper discusses historical data related to downhole scaling, corrosion and surveillance methods to identify affected wells. Efforts to minimize production impact due to increased corrosion seen late in the field life along with longer term corrosion mitigation efforts are also reviewed. Examples of how tubing was originally protected by thin film scale accumulation and emulsion flow during early field life production are also presented. Increasing October’s completion corrosion manageability is a key challenge facing the field. Addressing issues related to predicting future well failures and their associated production loss impact rig scheduling and procurement of expensive long-lead time completion material (Cr 13%).

The approved plan is to repair six wells per year over three years considering known well problems, remaining reserves, materials and rig availability. In early 2005, six well's were worked over and visual inspection of retrieved tubing showed an excellent match with caliper log data. The most severe corrosion is typically deep in the well and is related to high CO2 partial pressures. Corrosion risk to the casing has also been identified as potential issue and wall thickness assessments have been performed on some workovers. The paper reviews these items in greater detail and proposes forward plans for the remaining life of field.

Introduction:
October field is located in the Gulf of Suez (GOS) approximately 200 miles southeast of Cairo, Egypt. The field is operated by Gulf of Suez Petroleum Company (GUPCO) and currently produces 100 mbfpd at 65% water cut. Productive horizons include various sandstone formations at an average depth of 11,000’subsea. Most producing wells in the field are currently lifted by gas lift.

The field experienced severe downhole CaCO3 scaling across the sandface and completion equipment during its early life. High levels of calcium chloride in the formation water and large wellbore draw down led to numerous stimulations in the early 90’s. Scaling problems continued to increase until 1997 then dramatically decreased over a two-year period. The reduction in scale related well problems were clearly evident in the acid stimulation frequency of the field. This trend was unlike other analogous fields produced by GUPCO where CaCO3, BaSO4 and SrSO4 scale still continue today. Use of formation water rather than sea water, higher FBHP’s due to increasing reservoir pressure and water cut through water flooding, all contributed to the reduction of scale-related problems. To date, CaCO3 scaling problems have been practically non-existent in October field despite high water cuts (average 66.4%).

High levels of CO2 in the formation fluid and gas lift system (+3% mole fraction) along with increasing water cuts led to increasing corrosion related problems in the late 90’s. Efforts have been refocused in the area of downhole corrosion control and reservoir surveillance in order to maximize production and minimize cost during late field life. Recent changes in completion design include use of Corrosion Resistant Alloys (CRA’s) in an effort to mitigate the impact of CO2 corrosion.

Geology and Reservoir Properties
The main Nubia reservoir at October Field is massive oil wet carboniferous sand that has an average mid zone TVD datum of –11250 feet subsea (SS). Normal faulting has divided the field into several areas. The central part of the October Nubia is elongated six miles from the northwest to southeast. It is bounded on the western and southern sides by a large fault. The structure is further complicated by a number of smaller parallel splinter faults. (Fig.1).

The Nubia has five distinct sand layers classified as the TZ, MN, M-1, M-2A and M-2b. Each layer is separated by a continuous shale, and nearly all sands have shale or low permeability barrier that is relatively thin and discontinuous. The M-2 shale is continuous across the October Field and serves as the datum reference. These layers have 525 feet of gross thickness and 488 feet net pay thickness.