Modern formation pressure testing while drilling (FPWD) tools provide accurate formation pressure measurements, even under very challenging drilling and formation testing conditions. Pressure data from logging while drilling (LWD) tools are primarily used for drilling safety related pore pressure profiling, mud weight optimization and ECD controls. Its full potential in formation and reservoir evaluation has yet to be further explored. Pressure gradient analysis is a particularly costeffective solution for preliminary reservoir fluid evaluations while drilling or shortly after the well is drilled. Integrated with other LWD and surface logging data, pressure gradient analysis is able to provide valuable insight for planning subsequent fluid sampling, well completion and reservoir development programs which require accurate assessments of fluid types, fluid contacts, reservoir compartmentalization, and connectivity. Based on data and experience from recent worldwide FPWD and gradient jobs, we present a recommended best practice workflow for pressure gradient analysis using real time pressure testing data. The main procedures of the workflow consist of pre-job preparation, real time wellsite execution, quality control, statistics and error analysis, proper graphic presentation, data integration and interpretation. Special effort is made to identify fluid types, contacts, vertical fluid variation and reservoir barriers from pressure gradient analysis. It is found that the integration of pressure data with openhole logs and surface mud gas logging is particularly effective in reducing uncertainties in the interpretation. Possible factors responsible for departure from linear pressure gradient trend lines are discussed together with the limitations of gradient analysis. Quick reservoir evaluation in terms of fluid types, oil water contact (OWC), oil gas contact (OGC) and flow barriers can be obtained independently with the use of pressure gradient analysis from FPWD data. More reliable results are achieved by the integration of pressure measurement data with the openhole log interpretation, surface logging and offset well information collected in the pre-well planning stage as well as while the well is being drilled. Introduction For several decades, the pressure gradient plot has been used for identifying reservoir fluid types, contacts and reservoir connectivity (Chen, 2003; Steward et al., 1979, 1982). The information obtained from pressure gradient analysis has contributed to improved reservoir characterization and optimized completion and production strategies. Vast majorities of previous gradient work have been carried out with data from wireline formation pressure testing data and production logging tools (PLT). In recent years, increased usage of LWD formation pressure testing has broadened the spectrum of available raw data for pressure gradient analysis (Meister et al., 2003, 2004; Buysch et al., 2005).

Mud logging gas detection and chromatography have been traditionally used as indicators of hydrocarbon occurrence and wellsite safety. However, the application of mud logging gas as a reliable reservoir characterization tool had previously been hindered by its semi-quantitative nature, noticeably the inability to get repeatable responses in all environments so that the analysis can be used as a trusted analytical tool, regardless of gas trap operating conditions and surface environments.A new gas extraction system, Constant Volume Gas Trap (CVGT TM ), is now available at wellsite and has been successfully run worldwide. Equipped with several innovative features, CVGT not only improves mud gas extraction efficiency, but also reduces the effects of environmental and operation conditions on quantitative gas measurement. Coupled with high accuracy and a fast cycle gas chromatography system, CVGT gas ratio analysis provides a cost-effective approach to evaluate reservoir fluid types, contacts, and other critical information needed for subsequent fluid sampling, testing, and development programs.Several applications of gas ratio analysis are presented that complement other reservoir characterization tools and approaches. Vigorous data QC are enforced to reduce the effects of any non-reservoir fluid contributions. Most suitable ratio cutoffs are determined for the target reservoirs. These cutoffs are determined through a variety of factors, in particular the known reservoir fluid properties from offset wells in the area. C1/sum(C1~C5), and the combined use of gas wetness ratio (GWR) and light heavy ratio (LHR) have proved to be the most valuable out of all the gas ratios investigated. Together with total gas and gas chromatography, these ratios and ratio combinations are able to indicate the occurrence of reservoir zone, the types of fluid in it, and the fluid contacts. Fluid types defined from ratio analysis are correlated with LWD/wireline data, particularly the resistivity, cross-over of neutron and density, and pressure gradient analysis. This ultimately leads to better reservoir characterizations with regards to its vertical connectivity, compartment and caprock efficiency, etc.

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Formation testing, whether on wireline (WL) or logging while drilling (LWD), represents a challenging operation, which requires pre-planning, incorporation of local best practices, and good communication between the operator and the services company. Even considering the above practices, the success rate of acquiring representative pressure tests is limited, since formation artifacts such as sanding, washouts, or supercharging when testing in very tight formations can lead to misinterpretation. Today, many aging oil and gas fields are being redeveloped to target remaining hydrocarbon. Formation pressure, fluid gradients and the determination of whether or not compartments are in communication are important information when analyzing such a reservoir. This paper discusses an approach that facilitates understanding the above challenges while drilling, even in difficult environments. A smart test function reduces storage and shock effects while drawing down on tight formations, but also avoids sanding in highly unconsolidated formations. Performing self-learning, optimized test sequences improve the accuracy of the pressure and mobility data and lead to higher operating efficiency. The 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 accurate pressure data in real time warrants equal consideration, as a number of novel applications now exist. Case histories and recent improvements, such as testing on wired pipe or longer test times, are included in this paper and demonstrate the applicability to conventional formation pressure applications, such as compartmentalization evaluation or fluid gradient analysis, traditionally acquired with wireline formation testers. Benefits for drilling and subsurface teams, such as mud-weight (MW) management, safe selection of casing points, calibration of pore pressure predictions, selection of wireline sampling points, reservoir monitoring, geo-steering, and obtaining data in high-risk wells, are equally important and the reasons why LWD formation testing becomes a crossfunctional discipline. Introduction Wireline formation pressure testing has been routinely used as a valuable reservoir characterization tool and its results are generally well regarded (Chen 2003). Initially introduced primarily as a drilling safety and MW/ECD (equivalent circulating density) optimization enhancement through real-time formation pressure measurement, LWD formation pressure testing has yet to fully prove its effectiveness in reservoir evaluations. In recent years, as the result of continuing improvements in tool design and downhole technology, LWD pressure testing has gained more acceptance among reservoir engineers, geologists and petrophysicists. In cases where wireline formation pressure testing is unfeasible, such as in high angle and horizontal environments and with high rig costs to run wireline, LWD pressure testing provides an indispensable alternative to its wireline counterparts. Important information, such as reservoir fluid types, gas/oil/water contacts, and production and depletion history, can now be evaluated by LWD, thus providing timely data for preparing a completion strategy and design.