Sanjay Vitthal

A new machine classification method applied to human peripheral blood leukocytes

Human beings judge images by complex mental processes, whereas computing machines extract features. By reducing scaled human judgments and machine extracted features to a common metric space and fitting them by regression, the judgments of human experts rendered on a sample of images may be imposed on an image population to provide automatic classification.

New Breaker Technology for Fracturing High-Permeability Formations

Regained permeability studies with HEC polymer in high-permeability cores revealed that persulfate-type oxidizing breaker and enzyme breaker do not adequately degrade the polymer. Use of high concentrations of acid or peroxide breakers did show improved breaking, but additional work is needed to apply high concentrations of these breakers properly. Sodium persulfate breaker was found to be thermally decomposed, and its decomposition was accelerated by formation minerals. Enzyme breaker adsorbed onto the formation, but still partly functioned as a breaker. Dynamic fluid-loss tests with reduced-pH, borate-crosslinked gels suggest that accelerated leakoff away from the wellbore could be obtained through the use of a delayed-release acid. Rheological measurements confirmed that a soluble delayed-release acid could be used to convert a borate-crosslinked fluid into a linear gel. This conversion was visually confirmed by /tests involving a delayed-release acid and a borate-crosslinked fluid in a single-pass flow loop apparatus. Higher concentrations of breaker were placed in a borate-crosslinked fluid by encapsulating the breaker, and controlled viscosity reduction was obtained. A simulation using a 3D commercial simulator showed improved cumulative oil production when increased fluid loss from a soluble delayed-release acid was applied.

How Minifracs Alter Leakoff and Ways to Counteract It

The analysis of minifracs in high-permeability formations has been the subject of several studies and debates. In many cases, the leakoff from the frac-pack appears to be less than that from the minifrac, which is normally conducted before the frac-pack. Consequently, the net pressure rise observed is less than the predicted net pressure based on the minifrac analysis. Rules of thumb have been developed to account for this apparent change in leakoff behavior. These rules include adjusting the spurt loss, choosing a latter-time closure press ire based on previous experience, and adjusting the observed fluid efficiency by an arbitrary factor. This paper attempts to provide a rationale for explaining the discrepancy between leakoff data collected from minifrac analysis and the observed frac-pack behavior. This paper also presents the results of laboratory experiments and field tests that show that the injection of a minifrac alters the observed fluid efficiency. Laboratcry tests evaluated the magnitude and character of the fluid loss from subsequent injections of a frac-pack fluid. These tests were conducted with cores ranging from 100- to 3000-md permeability. Field results from trials in which two minifracs were injected in the same zone are also presented. These field data are from wells in the Gulf of Mexico (GOM) and from a well in North Africa, all of which experience high fluid-leakoffrates. The results from these injections show that the effects of minifrac fluid can alter fluid efficiency significantly. Finally, the paper proposes methods and best practices for measuring or counteracting this effect by altering the sequence of injections nto the formation. Laboratory data supports the philosophy behind these best practices. In addition, field data illustrate the success of this altered injection schedule.