Fig. 1—Example of the change-mapping technique applied to a core sample. The after-test image (a) shows a drilling mudcake attached at the top, which is not present in the before-test image (b). Image (b) is subtracted from image (a), leaving behind the change (c). A reservoir-conditions coreflood study was undertaken to assist with design of drilling and completion fluids for a Norwegian field. Multiple fluids were tested, and the lowest permeability alterations did not correlate with the lowest drilling-fluid-filtrate-loss volumes. This paper will examine the factors that contributed to alterations in the core samples. A range of measurements are made during reservoir-condition studies, with typical metrics of the performance of a fluid or sequence including the following: These metrics are unfortunately subject to a number of factors that make interpretation difficult and therefore add risks to the decision-making process. In order to reduce these risks, a number of interpretive techniques are used. These include scanning electron microscopy (SEM), thin sections, and computed-tomography (CT) scanning. In order to overcome some of the limitations posed by existing techniques, a micro-CT change-mapping technique was developed to show the distribution of alterations within samples at selected points in a study. This article, written by Technology Editor Chris Carpenter, contains highlights of paper , “The Nature of Drilling-Fluid Invasion, Cleanup, and Retention During Reservoir-Formation Drilling and Completion,” by and Corex; Aker BP; and University of Stavanger, prepared for the 2017 SPE Bergen One Day Seminar, Bergen, Norway, 5 April. The paper has not been peer reviewed. ... This article is reserved for SPE members and JPT subscribers. If you would like to continue reading, please , or
A research paper on the design of drilling and completion fluids for a North Sea oilfield found there was no direct connection between oil-based drilling-fluid-filtrate loss to the formation and formation damage caused by the drilling fluid. Damage is more likely to be caused by the drilling-fluid filter cake sticking to the formation, according to the study by the University of Stavanger, Aker BP and Corex. It recommends simulating the operational sequence at reservoir conditions, gathering information to interpret data, in order to minimise operational risk.