Study Of Recognition And Evaluation Technology On Low Resistivity Reservoir In Block H

With the deeper development of oil field exploration and exploitation and deepening understanding of oil and gas reservoirs, the low resistivity oil and gas reservoir has aroused wide attention. The low resistivity oil and gas reservoir, with extremely strong subtlety, has great potential in exploration. However, the recognition and evaluation of low resistivity oil and gas reservoir is difficult, considering of its complex formation genetic mechanisms. Because the low resistivity reservoir is easily being mistakenly considered as water reservoir or even being leaved out. Therefore, deep researches about formation genetic mechanisms of low resistivity reservoirs are necessary, as well as recognition and evaluation.Aimed at the difficulty of identifying and evaluating the low resistivity reservoir, the effort, in this paper, is systematically focused on the rock physical genetic mechanism of low resistivity reservoirs, basing on the geological environment analysis in M area of Algeria and Triassic reservoir of Tarim Basin. The low resistivity reservoir is recognized and the reservoir parameters are calculated separately, according to the different genetic mechanisms. Then, the low resistivity reservoirs are evaluated by the actual logging data.First, the genetic mechanism is summarized, including both geological and physical genesis, by geological backgrounds, well logging data, mud logging data, and large mounts of rock experiments. The geological genetic mechanism is analyzed from three aspects, tectonic setting, sedimentary characteristics and diagenesis. The physical genetic mechanism is emphatically analyzed, including main internal genesis, high immovable water saturation, high salinity formation water, and additional clay conductivity and main external genesis, sand shale sequence, and different water salinity between oil layers and water layers.For a particular area, low resistivity reservoir often has two or more kinds of the genetic mechanisms, leading to the difficulty of reservoir recognition. Therefore, the influences on resistivity of lithology, physical property, and salinity are momentous for low resistivity reservoir recognition with conventional logging data. In the paper, the differences in same formations physical property, electrical property, or non-resistivity factors are taken into consideration. The pressure gradient and fluid density of MDT logging and array induction logging new technique are used, as well, for low resistivity recognition.Shale content, porosity, permeability and saturation calculating method are built, basing on conventional logging, core analysis data and water analysis data, to provide reliable formation parameters in low resistivity reservoirs. The parameter QFM, calculated by Stoneley slowness, is related with the formation permeability. QFM is calculated and related to the equivalent porosity. Then the relationship between the QFM and equivalent permeability is built. For the reason that some wells don’t have core data, the pore index m is calculated by well logging information, containing shale content effect, for saturation calculation in shaly sandstone. The appropriate saturation calculating method is built basing on different low resistivity reservoir genetic mechanism. The Archie’s equation is mainly suitable for clean sandstones and high salinity water reservoirs. W-S model fits the clay minerals additional conductivity-based low resistivity reservoirs. The pore index m*and saturation index n*are calculated by the rock samples in the high cation exchange capacity reservoirs. At the same time, natural gamma ray logging and spontaneous potential logging are used to calculate the cation exchange capacity, and W-S model is effectively popularized and applied. In the paper, taking the fact of low resistivity logging response into consideration and avoiding the low resistivity effect on saturation calculation, the MDT logging data is used in calculating the oil column of the oil layer. Then the oil column is used for calculation oil saturation, with porosity and permeability data, to offer a reliable reservoir evaluation method.Finally the idea and technology of identification and evaluation on low resistivity reservoir are effectively applied in M area in Algeria and the Triassic reservoir of Tarim Basin, and they have played an important role in the future reservoir evaluation.