Igbani Sunday
In the late 20th century, reports of unsuccessful development and production of drilled wellbore and inaccurate estimation of proven and portable oil reserve were of concern to the petroleum industry. Consequently, research has focused on the evaluation of reservoir depletion degree on solution gas drive. But, most of these studies were conducted experimentally at simulated reservoir conditions. Few of these studies were conducted real-time using live data under reservoir prevailing conditions while drilling or producing. Moreover, data of equivalent mud weight (EMW) window logs were not investigated toward the prediction of reservoir depletion degree. Consequently, this paper used an EMW Window log of a single well of a Norwegian continental shelf oil reservoir located at the SST oilfield as a case study, to evaluate the depletion degree of the oil reservoir. The case study employed theoretical and analytical approaches to develop a model. The resulting model was used with the predicted reservoir depletion degree from the EMW window log and oil production performance log to establish a new method of reservoir depletion evaluation. These were achieved using Microsoft Excel 2010 and IBM SPSS as the data analysis tools. The results obtained from the model show that the reservoir depletion was at an average degree of 0.03% with an average pressure drawdown of 147 psi at the drilling stage, while at the oil production stage the reservoir depletion was at an average degree of 0.81% with an average pressure drawdown of 156 psi. The evaluated reservoir depletion degrees proportional relationship show that 27% of the proven oil reserve was recovered in the oil reservoir. These results evidenced that there exists a direct proportional relationship between the equivalent mud weight and pore pressure, while the reservoir depletion is inversely proportional to the pore pressure in an oil reservoir undergoing solution gas drive. This research demonstrates that the use of equivalent mud weight in the evaluation of reservoir depletion degree would lead to a multi-disciplinary approach to reservoir characterisation and management that would maximize oil recovery and improve the design of upstream oil and gas surface equipment.
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