This paper presents a novel methodology to successfully maximize sampling and scanning of formation fluids using formation mapping-while-drilling (FMWD) technology in real time when drilling poorly consolidated formations. The methodology, based on a solid workflow built on experience garnered and captured in various operations and geomechanical studies performed around the world, can be applied in a wide range of wellbore geometries and formation types.
The methodology is based on four processes: 1. Predict, assess, and confirm potential fines migration and formation collapse during FMWD operations. The analysis is based on processing and interpreting existing geomechanical properties from offset wells and real-time newly acquired sonic and/or density data. 2. Design FMWD operations such that formation sanding is prevented, and formation integrity is maintained. 3. Prevent mobilized fines from entering the FMWD tool if partial formation collapsing occurs. 4. Focus the workflow on reducing the negative impact solids will have on the flowline, pump out, and optical analyzers if fines enter the tool.
The paper contains two case studies in which the methodology workflow resulted in successful sampling and real-time downhole fluid analysis of formations with very limited diagenesis and a history of sanding and collapsing during formation testing-while-drilling operations. These two case studies show how assessing offset wells during the planning phase and applying this workflow while evaluating logging while drilling (LWD) petrophysical data in real-time provide a quick insight into how a formation will respond during pump out. The results define station depth selection, timing of the operation with respect to wellbore exposure time, and pump out rate strategy. The application of fixed-rate pump out or intelligent pump out with a fixed differential can then be applied based on the real-time indicators. Specific screen sizes are selected in advance, which limit ingress of fines into the sampling tool. In both case studies, the operating company's objectives were met. An additional case study is presented in which the risk of sanding was not perceived, and no qualification of un-consolidation had taken place, ultimately resulting in formation breakdown in the sampling phase, mobilization of fines, and plugging of the tool; thus, highlighting the value of the novel methodology.
The innovation of this workflow is its holistic approach to sampling while drilling in unconsolidated formations, extensively covering both job planning and execution phases. Additionally, the workflow allows for optimizing tool configuration, and by risk identification, suggests a variety of measures to eliminate or mitigate the impact of partial formation collapse. This workflow extends the application of fluid mapping and sampling while drilling into operational environments, which were previously considered highly unsuitable for this technology.
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.
Smart Technology - Reliable Performance
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.