Knowledge of bubble point pressure is very important in reserve estimation and other petroleum engineering calculations such as modeling of fluid flow through porous media and multiphase flow in pipes. Usually, this property is obtained from laboratory PVT analysis. However, when such analysis is not available, empirically derived PVT correlations are used. This work focuses on the use of an Artificial Neural Network (ANN) to address the inaccuracy of empirical correlations used for predicting bubble point pressure. The ANN is a mathematical model inspired by biological neural networks. In this modeling approach 1248 data sets collected from the Niger Delta Region of Nigeria were used. The data set was randomly divided into three parts, of which 60% was used for training, 20% for validation, and 20% for testing. The accuracy of the new Artificial Neural Network was compared with existing empirical correlations. The ANN model outperformed the existing empirical correlations by the statistical parameters used with a best rank of 17.3132 and better performance plot.
The completion cost of development wells is usually 30-50% of the Authority for Expenditure (AFE). This depends on the number of zones to be completed, the completions strategy, cost of downhole jewelries and complexity. The quest to develop these complex un-stacked reservoirs has increased the tortuosity of the well plan and the complexity of the wells. This has in turn increased the completion complexity and has significantly increased the time taken to deploy the completion accessories, and the time taken to set the packer. The sand management strategy and lower completion philosophy for the case study field, is setting Stand Alone Screens (SAS) as the lower completion assembly. Over the years, Addax Petroleum has used the metallic ball to set the lower completion production packer in a slightly straight well. Due to the need to optimize the well architecture and the tortuous profile of the well, the average production packer is now set at circa 80-85 degree's inclination. This optimization plan, significantly increased the amount of time required to circulate the metallic ball to the lower completion ball seat (a device engineered to aid the setting and hanging of the lower completion assembly in the production casing). This increase in time has further increased the completion costs. To ensure that the development cost is reduced due to the current unstable and low oil price, a plastic setting ball (with lower specific gravity) was identified, risk assessed and used successfully to significantly eliminate the excess time for completion operations. This paper reviews the challenges experienced using the metallic packer setting balls in highly tortuous horizontal wells. It also shows and discusses the huge cost savings achieved in case study wells where the low gravity packer setting ball was used to set the lower completions production packer.
With the recent decline in price of crude, more cost effective ways are explored to ensure that the production rates are sustained and increased. The need for cost effective subsea well intervention has been discussed and documented over the last few years. The increasing number of installed subsea wells combined with the increasing age of subsea fields continues to drive demand for more efficient subsea well intervention. Traditionally the accessibility to subsea wells is considered more difficult and represents a large cost compared to wells with direct platform access. Even minor jobs represent large expenses, leaving a gap between intervention frequency on subsea wells and wells with direct platform access. The average recovery rate for a subsea well is considerably lower than that of a comparable surface well due to the relatively more complicated well intervention and maintenance issues. Using heavy and traditional rigs for subsea intervention is costly and time consuming due to the high day-rates and mobilization aspects. The base costs are therefore considerable higher as compared to surface well intervention where tools can be deployed directly through the risers from the production unit. At Addax Petroleum, Nigeria, the re-entry and intervention of existing poor producing subsea wells was identified as a cost effective method to maintaining production in the reasonably high cost oil subsea environment. However the major challenge with subsea intervention is the uncertainty that surrounds the planning and operations which grows exponentially with the age of the well. As factors like corrosion, and well integrity (cement and casing) all become critical in the successful delivery of the well. The availability of required service equipment and modes of operation also become very critical especially for old and obsolete Subsea equipment. There is always a significant extra cost spent if any of the identified or unidentified risks manifest. In 2014 Addax Petroleum embarked on a successful re-entry campaign as part of the second phase of its Okwori Field Development Plan. This paper highlights on the lessons learned from the campaign, discussing the challenges, planning, and execution phases of the successful well re-entry campaign in deep water operations.
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