This section of the present disclosure is intended to introduce the reader to various aspects of art that may be related to various aspects of the subject matter described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this context, not as admissions of prior art.
The present disclosure relates generally to techniques for estimating continuous fluid properties from well logs obtained within a subsurface Earth formation. Such fluid properties may include, for example, water salinity, water saturation, and hydrocarbon types and properties thereof.
Well logging instruments have long been used in wellbores to make, for example, formation evaluation measurements to infer properties of the formations surrounding the wellbore and the fluids in the formations. Common logging tools include electromagnetic (resistivity) tools, nuclear tools, acoustic tools, and nuclear magnetic resonance (NMR) tools, though various other types of tools for evaluating formation properties are also available. Early logging tools were run into a wellbore on a wireline cable after the wellbore had been drilled.
Modern versions of such wireline well logging instruments are still used extensively. However, as the demand for information while drilling a wellbore continued to increase, measurement-while-drilling (MWD) tools and logging-while-drilling (LWD) tools have since been developed. MWD tools typically provide drilling parameter information such as weight on the bit, torque, temperature, pressure, direction, and inclination. LWD tools typically provide formation evaluation measurements such as resistivity, porosity, NMR distributions, and so forth. MWD and LWD tools often have characteristics common to wireline tools (e.g., transmitting and receiving antennas, sensors, etc.), but are designed and constructed to endure and operate in the harsh environment of drilling.
In current volumetric estimation techniques, petrophysical properties of water and hydrocarbons are assigned assumed values and are input into a numerical solver for estimation of volumetric properties within a formation. Often, the petrophysical properties are not all known. For example, examples of unknown properties can include water salinity and varying hydrocarbon type/grade column. In these cases, formation testers can be used to collect fluid samples, perform downhole fluid analysis, or infer fluids type from pressure gradients. The outcome of any such analysis or testing depends on the selection of test depths, which inherently contains hypotheses of the fluids in place. Some known techniques provide for the estimation of continuous water salinity and/or saturation, but do not address the unknown hydrocarbon types and properties. Hence, there is a need for continuous estimates of water and hydrocarbon properties from well logs.