Horizontal well technology has provided the oil industry a new method of optimising production from brown fields, which would otherwise have been uneconomical to further develop. These fields are characterised by complex fluid displacement behaviours, gas/water coning, declining oil production, differential flushing e.t.c. In order to further develop these fields, with its associated challenges, the land asset team in conjunction with the well engineering department of SPDC-East in Nigeria recently embarked on the drilling of horizontal short radius sidetrack wells from existing wells. The campaign, at maturation was forecasted to add some 32Mbopd and develop 53MMstb reserve through construction of wells that are capable of delivering over 2,000bopd, at maximum of $1.5Mln. Given the anticipated scope of work, a campaign approach in two phases was endorsed. To date, a total of 10 wells (in Dalume & Boloma North fields) have been drilled. Several challenges were encountered during the campaign. These include present fluid contacts delineation in producing brown field reservoirs, data acquisition in a high dogleg severity wells (17 - 35deg/100ft), depth tie-in/control at sidetrack point and accurate well placement in thin oil columns. Some of these challenges were resolved by acquiring cased hole fluid contact monitoring data (Schlumberger's RST) prior to start of campaign and taking gyro surveys with proper well correlations at sidetrack point The application of the MWD tool response modelling module in LOGIC also helped in proper "Petro"steering and post-mortem of the drilling operations. The result of this campaign show that about 20,000bopd tested production potential have been added with over 20MM stb developed in the project first phase. During the campaign, a significant reduction in cost of well delivery from $2.6Mln (first well) to some $1.5Mln average in the last four wells on the sequence was achieved. Some innovative completion methods were implemented primarily to reduce cost and improve well delivery. For instance, a combination of ESS and ECP was deployed for the first time in medium radius wells worldwide. This paper focuses on the petrophysical challenges involved in the planning and execution of the wells using short-medium radius technology. It emphasizes data acquisition issues in high dogleg wells, anomalous fluid contacts movements in brown fields and the use of resistivity tool response modelling in placement of horizontal wells in thin oil columns. The report presents the technical analysis of the challenges and results of the petrophysics input and contribution to the short radius sidetrack campaign in Shell Petroleum Development Company Limited, Nigeria.
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