High resolution wellbore imaging, deep and extended-range focused resistivity, and the ability to provide azimuthal quadrant resistivity measurements while sliding are key features of a new 175C rated laterolog resistivity imaging while drilling tool that has already generated impact in China. This paper presents field application examples from different fields in China to show how the new technologies are solving field development challenges and generating significant cost savings for the operators.
The azimuthal laterolog resistivity imaging tools (RIT) in both 6.75-in and 4.75-in collars have been used to acquire logging-while-drilling resistivity and wellbore image logs in more than ten wells in the Sulige Gas Field, Changqing Oilfield, and Jidong Oilfield, addressing formation evaluation needs in, heterogeneous, low-porosity, or low permeability and other complex reservoirs. Excellent agreement has been achieved between the logging-while-drilling resistivity measurements from the new tool and traditional wireline resistivity logs, when available. High-resolution wellbore images from the tool have been utilized to more accurately delineate formation layers and to determine the reservoir thickness. Borehole breakouts from wellbore images are also used to aid wellbore stability and geomechanical analysis. In a high angle well in Jidong Oilfield, wellbore images while drilling reveal how the wellbore enters and exits the dipping formation layers, demonstrating the ability to describe accurately the formation structures and to optimize the placement of well trajectories.
In Qinghai Oilfield, the high-resolution wellbore images from the LWD tool are utilized to characterize the complex geology in the presence of extensive faults, fractures, and complex folds, providing the same types of information that is traditionally obtained only from wireline electrical images. The ability to characterize formation geology while drilling, presents significant opportunity in operational time and cost savings in high angle wells by eliminating wireline trips which could take up to one hundred hours to run.
In Southwest China, complex geological structures, high tectonic stresses, and over-pressured and fractured reservoir formations in the field coupled with above 150C downhole temperature present a huge challenge to drilling and logging programs. Wireline logs typically cannot be obtained due to the risk of wellbore instability. Understanding formation type and geological structure, and characterization of complex dolomite karstic such as caves, vugs and fractures are important for well placement and field development. Wellbore images while drilling from the 4.75-in collar tool have been used instead to characterize the reservoir types and identify unique characteristics in different formations. In addition, the tool's ability to measure very high resistivity in the range of thousands of Ohm-m in conductive mud, allows proper delineation of potential pay zones from anhydrate formation, meeting the logging requirement for the wells. The integration of deep resistivity, wellbore images, and azimuthal gamma ray measurement into the same collar and it's HTHP rating, makes this logging-while-drilling tool a versatile sensor to include in any bottom-hole-assembly to aid accurate formation evaluation and well-placement applications.