Study Of Recognition Technology And Distribution Law On Low-resistivity Oil Reservoir

As strongly subtle and special oil and gas reservoir, the low-resistivity pay has enormous exploration potentiality. But because of its complex geologic genesis, the low-resistivity pay is very difficult to indentify and evaluate. Aimed at the question of indentifying and evaluating the low-resistivity pay, this paper systematically summarizes the internal genesis and external genesis of low-resistivity pay by analysising the results of enough rock experiments and collecting the log response of typical low-resistivity pay. The internal genesis mainly include high bound water and high cation exchange capacity, and the main external genesis are mud invasion, sand shale sequence and different water salinity in oil/water layers, each kind of genesis is link to the peculiar geologic condition. To a certain area, the genesis are wildly existed, but only one or two is the major genesis which effect the resistivity of oil and gas layers. Therefore, it is developed that the approach and scheme of identifying and evaluating the low-resistivity pay based on the major genesis, the design concept and principle of log system and environment are established, and many new methods based on the major genesis and conventional logging data are proposed. Those new methods are as follows:①A new technique of recognizing low-resistivity pay by SP is first proposed, it is based on optimizing design of drilling-mud property,.oil reservoir has low amplitude positive or negative SP anomaly under brine mud.②The axis of crossplots of identifying oil layers represents integrated parameters, on this parameters, lithology, salinity and mud are considered. This parameters enlarged micro-difference between oil and water layers, two of this parameters are used to identify low-resistivity pay.③According to the difference on the main genesis, this paper develops and improves Archie's Model. Aimed at low-resistivity pay due to fine lithology, complex pore structure and the changed salinity, this paper has established empirical formula between parameters in the model (m, n) and shale content, porous structure exponent, formation water resistivity. Archie's Model is used to calculate saturation of low-resistivity pay by considering main control factors into model parameters.④This paper supplements and popularizes W-S Model. According to low-resistivity pay with higher cation exchange capacity, this paper establishes the relationship between Bws and temperature based on the experiment results of rock resistivity in various temperature, and calculates cation exchange capacity and water resistivity by induced polarization log data. So W-S Model can be applied.⑤This paper has also proposed an identification principle combined well-logging and geology: stratigraphic position separation, fine division of interpretation unit and reasonable stratigraphic correlation.⑥New well technology plays an effective role in recognition of low-resistivity pay. In a word, the idea and technology of identification and evaluation on low resistivity pay are effectively popularized and applied in Jidong Oil Field, and they have played an important role in exploration and reserve confirmation.