RIASSUNTO
IADC and SPE Member
Introduction
Risk sharing and alliance formation are central themes,in the E&P business environment of the 1990s. A common manifestation of these themes is the recruitment and use of partners and contractors to perform drilling operations on specific projects which formerly would have been 100% managed and operated by large integrated oil companies. One consequence of risk-sharing activity is that integrated companies have had the opportunity to closely observe and assess the drilling practices of other operators and incentive-oriented drilling contractors on wells in real time, with funds at risk.
The debate over which kind of business organization and risksharing philosophy produces the most cost-effective drilling result often neglects the fact that for any given well, the in-situ conditions would be identical for anyone undertaking the work. There is no inherent logic in the notion that turnkey contractors have an edge on oil companies in addressing subsurface conditions. The economic outcome of a given well is more dependent on objective subsurface factors and the way they are approached than on the kind of risk-sharing philosophy selected for drilling. Similarly, there is no inherent logic in the notion that hiring a turnkey contractor absolves an oil company from risk on a well. At a minimum, the risk of possible production delays caused by acts of a turnkey contractor is always present.
Three wells (A, B, and C) drilled recently illustrate the point. One well was drilled by an oil company and two were drilled by turnkey contractors. All three wells penetrated geopressured sections. The resulting geopressure-related problems with fracture gradients and wellbore integrity caused large economic impacts on turnkey drillers and operators alike. The wells were selected to highlight the common-sense idea that the key to risk management and achieving profit goals is good planning and proper execution, not the form of risk-sharing selected for any particular venture.
This paper examines the boreholes, explores relationships between planning and execution during drilling operations, and explores the economic impacts of geopressure problems on financial outcomes and decision choices on geopressured wells. Conclusions are drawn from experiences on these wells and recommendations are made on approaches to minimizing the problems caused by pore pressures and fracture gradients.
Background and Methods
Figure 1 illustrates the drilling time required for each well to reach particular depths. Clearly0 Well A experienced the least trouble of the three. Not incidently, Well A was maybe the least physically challenging of the prospects to drill. Well B features two hole sections that were re-drilled after fish were left on bottom following well control incidents. The first was a kick taken at 11,752'. The second was a problem with gas cutting and flow at 16,932'. Well C presents the longest history of the three and was the only well not to reach projected total depth. This well experienced lost circulation below 11,525'. A drill string failure at 14,177' resulted in a side-tracking operation. A stuck pipe incident at 14,579' caused a second side track. Well control problems at 16,269' and 15,953' caused third and fourth side tracks. The well was finally abandoned after drilling the fourth side track to 14,032'.
What went wrong with each of the three wells? Analysis of information gathered during drilling operations provides insights into the well planning process and also illustrates the dominant impact of pore pressures, fracture gradients, and effective stresses on the success or failure of drilling operations.
All pore pressures and fracture gradients were calculated from wireline-log data using the Eaton Method. Compaction trend analysis generally follows the guidelines of Magara. All computed curves were checked for consistency with pore pressures and fracture gradients actually measured in the wells during drilling operations. Sonic and resistivity logs were used and good agreement (generally within 0.2 ppg E.M.W.) between pore pressures calculated from each log was obtained.
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