Improved Formation Evaluaton Using Azimuthal Porosity Data While Drilling

Abstract

Measurement of formation porosity and lithology in azimuthal quadrants around the borehole is now available. This new information is provided by a nuclear tool that makes azimuthal density, photoelectric factor and neutron porosity measurements while drilling. In addition, an ultrasonic sensor provides a tool standoff measurement in each quadrant. While rotating, the quadrants are defined by a magnetometer and oriented with the gravity vector, so that bottom, left, right and top quadrants are identitled.The tool Cim be run with several different stabilizer sizes or without a stabilizer, giving the driller more latitude in configuring the bottomhole assembly. The azimuthal capability allows the measurement of porosity with an unstabilized or "slick" tool without degradation of the measurement. This is accomplished by computing the porosity from the bottom quadrant where there is little tool st,mdoff in deviated or horizontal wells. Utilizing bottom quadrant porosities also results in improved measurement accuracy in cases where borehole conditions are poor due to enlargement or washouts. When the tool is stabilized, the quadrant porosity and lithology measurements result in improved geosteering as well as providing a quantitative measure of formation heterogeneity. At bed boundaries, comparison of top and bottom logs in real time results in better bed boundary detection and confirmation of the tool location within the pay zone. When the tool is between boundaries. an beterogeneity indicator can be computed from the quadnmt density, lithology and neutron porosity logs to better evaluate complex formations.The measurement of tool standoff per quadrant provides information on borehole size, shape and rugosity. The data can be used to indicate borehole stability on subsequent bit trips.The paper describes the method of the measurement. h,u'd- 137ware implementation and log examples illustrating the tool features.

Nuclear Logging-While-Drilling Measurement: An Assessment

“…(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15) These follow the recognition that nuclear LWD measurements have features which are significantly different from those of wireline measurements. Table 1 lists a few of these differences.…”

“…(5,9) The resultant correction is applied to the neutron sonde. This tool also uses a magnetometer to locate the bottom of the hole in a deviated well.…”

“…(9) This technique is used with design 1 cited in Table 2. The standoff from the ultrasonic caliper can be used to correct the neutron sonde.…”

Inversion-based method for interpretation of logging-while-drilling density measurements acquired in high-angle and horizontal wells

“…Inversion methods introduced in this paper focus on measurements acquired with a commercial LWD density tool. Accordingly, we consider an azimuthal binning scheme divided into 16 sectors, each subtending an angle of 22.5°from the center of the tool (Evans et al, 1995;Holenka et al, 1995). Furthermore, we assume that a measurement acquired with a given sector represents average angular LWD density measurement within that sector (Uzoh et al, 2007).…”

Hole Shape from Ultrasonic Calipers and Density While Drilling - A Tool for Drillers

“…Caliper information has been available for a number of years from Logging While Drilling tools 1,2 . These are all derived measurements rather than a physical measurement of the borehole size.…”