Abstract
The demand for low cost but reliable technology in drilling, logging and production is always and will continue to be one of the most important issues facing the oil industry. In addition, increasing production through field management and evaluating bypassed reserves in existing fields using lower cost but reliable technology is a primary objective of any oil company. From this motivation, a through casing log interpretation technology for assessing formation evaluation and identifying existing field opportunities would offer a low cost and risk option for many operations.
In this paper, a through casing log interpretation technology termed Lithology Independent Porosity and water Saturation or, LIPS, is presented. LIPS is a technology that is suitable for infill drilling programs, fluid monitoring for field management and in analyzing old fields that do not have enough or modern data. LIPS requires three measurements to provide porosity, water saturation and the locations of the heavy minerals that may be the source for net pay determination. These three measurements can be obtained using the three common cased hole logs; a thermal Compensated Neutron porosity Log or CNL, an epithermal neutron porosity and a Pulsed Neutron Capture log PNC type tool, e.g., TDT, for formation absorption cross section.
For porosity, LIPS considers any formation as a composite of two major components, the pore space and the matrix. LIPS deals with the matrix as a black box where it calculates its overall controlling parameters. The formation porosity is chosen when the calculated parameters using two different techniques converge.
For water saturation, LIPS uses data that has been discarded by the industry, the thermal neutron detectors counting rates of the thermal neutron tool. These counting rates are functions of the formation water salinity and the matrix absorption cross section. LIPS uses the two thermal neutron counting rates, near and far, of the thermal neutron tool CNL along with the formation absorption log to produce three equations in three unknowns. The three unknowns are water saturation, water salinity and matrix absorption. Therefore, LIPS does not require prior information about matrix absorption or the formation water salinity which gives LIPS superiority to many of the existing water saturation models.
LIPS has been tested in a variety of reservoirs from all over the world. Comparisons between LIPS porosity and water saturation and core porosity and low invasion water saturation core are presented. Also, the environmental effects on LIPS interpretations, e.g., invasion, are discussed.
