New Techniques in LWD Formation Pressure Testing Enable Real-Time Reservoir Evaluation in Evermore Challenging Environments

Abstract

Wireline formation pressure testing has been routinely used as a valuable reservoir characterization tool and its results are generally well-regarded. On the other hand, LWD formation pressure testing, initially introduced primarily as a drilling safety and equivalent circulating density (ECD) optimization tool, has yet to fully prove its effectiveness in reservoir evaluation, due to perceived data acquisition challenges. Today, re-entry drilling is used in many aging oil and gas fields to target the remaining hydrocarbon. Formation pressure, fluid gradients and the determination of whether or not compartments are in communication are important information when analyzing such reservoirs in real time for optimum wellbore placement. The cost efficiencies of acquiring formation pressure data while drilling are becoming more influential in the operator's technology selection process, but should not come at the cost of reduced data accuracy or data usability. This paper discusses new techniques and technologies that facilitate gaining a better understanding of the subsurface while drilling. These include a smart test function, which reduces formation shock while pressure testing in microDarcy formations and avoids sanding in highly unconsolidated formations. Performing optimized test sequences improves the accuracy of the pressure and mobility data and leads to higher operating efficiency. Further to this, LWD pressure testing on wired pipe yields a data density previously only found on wireline. The introduction of extended test times of up to 40 minutes broadens the scope of LWD pressure testing into traditional formation pressure testing applications, such as compartmentalization evaluation or fluid gradient analysis. Longer test times and testing on wired pipe precede future fluid sampling while drilling. Benefits for drilling and subsurface teams are equally important and one of the reasons why LWD formation testing has become a cross-functional discipline. Case histories from the Middle East will be used to highlight the recent technology advances and applications. Pressure Testing in Highly Unconsolidated Formations One of the extreme challenges for formation testers is pressure testing in highly unconsolidated sand formations due to different reasons, varying from formation strength over pad size and formation break-in during testing. Furthermore, the testing procedure has a big influence on the success of a pressure test. In the following sections, we discuss these effects in more detail.

Automation in Wellbore Stability Workflows

“…To some extent, a preliminary analysis or interpretation can also be carried out downhole. One example for the automatic interpretation of downhole acquired data includes formation pressure testing (Hahne et al, 2009). The authors present a smart test function for formation test reduction while pressure testing to gain a better understanding of the subsurface.…”