Real-Time Reservoir Characterization and Geosteering Using Advanced High Resolution LWD Resistivity Imaging

Abstract

A recently introduced azimuthal resistivity LWD imaging tool has been upgraded with advanced high resolution sensors that are capable of differentiating reservoir and borehole features down to a size of 0.4 in. when drilling in well consolidated formations. The high vertical and azimuthal resolution, along with 100% borehole coverage, yield an image quality comparable to that of wireline service for applications that include fracture characterization and formation evaluation. This paper describes a field test of the high resolution tool in 5 7/8" and 8 3/8" holes in Saudi Arabia and shows the application of LWD images for estimating carbonate reservoir producibility involving the characterization of secondary porosity. The LWD imager provides significant economic and logistic benefits, especially in slim horizontal sections; in addition, it can identify fractured zones with mud loss potential shortly after penetration. The real-time resistivity provides a good basis for accurate dip calculation and geosteering in general. In its default configuration, the high resolution tool is equipped with six high resolution sensors arranged in two rows. One of the benefits of the multi-sensor configuration, demonstrated by the field test, is the ability to validate the image quality by comparing data from various sensors. Another benefit is the depth correction achieved by correlating images from identical sensors located at various depths. The paper also discusses the fundamental principles behind high resolution resistivity imaging in conductive mud and makes extensive use of modeling techniques to characterize the sensor performance in various practical situations.

A Numerical 1.5D Method for the Rapid Simulation of Geophysical Resistivity Measurements

“…Substituting (8) into (7) and applying the change of coordinates under the integral signs, we obtain:…”

“…We categorize these resistivity prospection methods according to their acquisition location as (a) on surface, such as the ones obtained using controlled sources electromagnetics (CSEM) [1][2][3] and magnetotelluric [4], and (b) in the borehole, such as the ones obtained using logging-while-drilling (LWD) devices. LWD is a technology that conveys borehole logging tools (e.g., gamma ray, resistivity, density, and sonic) downhole, record measurements, and transmit them to the subsurface for real time interpretation while the hole is being drilled [5][6][7][8][9][10][11][12]. These tools provide two pieces of information: (a) real-time data, which is processed on the field while drilling, and (b) data that is stored in the device to process after pulling it out from the hole.…”

“…These tools provide two pieces of information: (a) real-time data, which is processed on the field while drilling, and (b) data that is stored in the device to process after pulling it out from the hole. We use real-time data to evaluate the formation for geosteering, which is the act of adjusting inclination and azimuth angles of the borehole to reach a geological target [5][6][7][8][9][10][11].…”

“…They were commercially used for formation evaluation, especially in high-angle wells. Nowadays, LWD devices are used both for reservoir characterization [6][7][8] and geosteering applications [9][10][11]. Modern borehole resistivity instruments can measure all nine couplings of the magnetic field, namely xx, xy, xz, yx, yy, yz, zx, zy and zz couplings (the first letter indicates the orientation of the transmitter and the second one indicates the receiver orientation) [13,14].…”

Reservoir Characterization, Fracture Mapping, and Well Placement Using a Suite of Logging-While-Drilling Images with Multiple Resolutions in a Marginal, Middle East Carbonate Reservoir

“…A recent development in azimuthal focused resistivity is the upgrade of some of the sensors to an even finer pixel resolution of 0.4 × 0.4 in. (Al-Musharfi 2010). This resolution is critical for identifying fractures, faults, and thin laminae of mud stones.…”