The potential operator cost efficiencies of acquiring valid formation pressure data while drilling are becoming more influential in deciding the value proposition of a wireline reservoir characterization program. Cost efficiencies may indeed be pivotal but importantly, the benefit of acquiring pressure data in real time needs equal consideration, as a number of novel applications now exist.
The paper will use case histories and lessons learned from experience with 300 logging while drilling (LWD) formation pressure runs in different operating areas including Asia Pacific to demonstrate the applicability to conventional formation pressure applications, traditionally acquired with wireline formation testers upon reaching section or well total depth (TD). These are the determination of formation pressure, fluid contacts, reservoir connectivity, and near-wellbore mobility. We discuss novel real-time applications and benefits for drilling and subsurface teams, such as mud weight management, safe selection of casing points, calibration of pore pressure predictions, selection of wireline sampling points, reservoir monitoring, geosteering, and obtaining data in high-risk wells.
Incorporating formation pressure testing into the drilling process presents challenges to perform measurements in a timely manner, as well as the need for continuous circulation while testing to ensure wellbore safety.
Providing this type of while-drilling formation evaluation data with an LWD tool allows a continuous approach to data evaluation and decision-making. The ability to measure accurate LWD formation pressure data in a variety of hole sizes represents a significant opportunity for safe and cost-efficient wellbore construction, especially in challenging environments.
With the introduction of LWD formation pressure testers, it has become possible to acquire formation pressure and mobility data during short breaks in the drilling process. Formation pore pressure and near-wellbore mobility are key parameters for reservoir description. Traditionally, these data are acquired with wireline formation testers upon reaching section or well TD. In high-angle wells, this is a time-consuming operation, as the tools must be conveyed by drillpipe. Providing this type of formation evaluation data with an LWD tool allows for a continuous approach to data evaluation and decision-making and represents a significant opportunity for safe and cost-efficient wellbore construction.
The success of the discussed LWD formation tester is in particular based on smart, self-learning operating processes, which improve the accuracy of the pressure and mobility data as well as the sealing success rate. In addition to mobility-dependent test times, this smart test function reduces shock effects while drawing down on tight formations and also avoids sanding in highly unconsolidated formations.
The precise control of the drawdown pump allows the optimization of the individual pressure test sequence. The drawdown process is governed by the drawdown rate and volume being applied to the formation by the pump system in the tool. In order to achieve valid pressure tests quickly, both parameters need to be optimized for the mobility and pore pressure encountered in the formation being tested. However, pressure may differ from expectations and mobility may vary over several orders of magnitude, which requires that drawdown rate and volume parameters be adjusted between individual pressure tests.
Intelligent pad control allows individual and continuous control of the test cycle and the drawdown pump. A closed-loop control of the pad contact force enables optimum sealing efficiency, saving significant time for "lost seal" retesting and avoids formation damage. Initial LWD formation pressure test results have been good. However, the drive has been to decrease test times and improve seal success and accuracy. Fig. 1 shows the improvement (global basis) in seal success since the introduction of the discussed smart technologies1.