A Dual-Porosity, Surface, and Matrix Electrical Conduction Model for Low-Contrast Resistivity Sandstone Formations

DC conductivity, cationic exchange capacity, and specific surface area related to chemical composition of pore lining chlorites

“…Effect of clays' CEC, such as smectite, illite, and kaolinite, on resistivity measurements of sandstones has been widely studied in the literature and has contributed in the building of well-known log interpretation models [3][4][5][6][7]. Even the models that do not deal explicitly with CEC [8,9] take into account the intrinsic conductivity of these clays. However, these properties have not been studied widely in chlorites.…”

Generalized effective medium resistivity model for low resistivity reservoir

“…Givens et al [1,2] presented experimental data from two core samples for low resistivity reservoir (No.1, No.2). The effective porosity of the samples is 12.8% and 11.4% respectively, capillary bound water saturation varies from 20.0% to 30.0%, water saturation from 0.32 to 1.0 and 0.4 to 1.0, and water conductivity is 0.137409 Ω·m and 0.045362 Ω·m.…”

“…Many analysts have studied geneses of low resistivity reservoirs in detail. Their achievements show that low resistivity in shaly sands can be caused by intrinsic factors, extrinsic factors and complex factors [1][2][3][4][5][6][7][8][9][10][11][12][13] . Intrinsic factors include high saline formation water, high irreducible water saturation caused by microscopic capillary pores, excess conductivity of dispersed clay, conductive minerals in rock matrix and thin sand-shale interlayers.…”

“…Because effects of extrinsic factors on log interpretation accuracy are decreased to some extent by selecting right drilling conditions and formation water resistivity, and correcting for invasion effect, only intrinsic factors should be considered in establishing a generalized resistivity model for low resistivity reservoirs. Until now, resistivity models applied in low resistivity reservoirs are mainly as follows: 1) Archie equation [14] , applied in low resistivity reservoir caused by high saline formation water; 2) electric double layer resistivity models [15][16][17][18][19][20] , applied in low resistivity reservoir caused by high saline formation water and excess conductivity of dispersed clay; 3) conductive rock matrix models [1,2] , applied in low resistivity reservoir caused by high saline formation water, microscopic capillary pores, conductive minerals or clay in rock matrix; 4) three-water conduction model [21] , describing conductance mechanism for low resistivity reservoir better, and applied in low resistivity reservoir caused by high saline formation water, microscopic capillary pores, and excess conductivity of dispersed clay; 5) dual water clay matrix conductive model [22] , applied in low resistivity reservoir caused by high saline formation water, microscopic capillary pores, and excess conductivity of dispersed clay; 6) effective medium HB resistivity model in laminated and dispersed shaly sand [23 -25] , applied in low resistivity reservoir caused by high saline formation water, excess conductivity of dispersed clay, conductive minerals in rock matrix and thin sand-shale interlayers; and 7) symmetrical effective medium resistivity model in laminated and dispersed shaly sand [26][27][28] , applied in low resistivity reservoir caused by high saline formation water, excess conductivity of dispersed clay, conductive minerals in rock matrix and thin sand-shale interlayers. To sum up, since resistivity models in current use cannot completely describe conductance mechanism in the complex hydrocarbon-bearing reservoirs, especially when dispersed clay, laminated shale, conductive minerals in rock matrix, microscopic capillary pores, and high saline formation water coexist in hydrocarbon-bearing shaly sand reservoir, conductance mechanism in the complex hydrocarbon-bearing reservoir becomes more complicated and a generalized resistivity model is needed to describe the conductance mechanism for low resistivity reservoir with presence of the five intrinsic factors.…”

Analyzing the Origin of Low Resistivity in Gas-Bearing Tight Sandstone Reservoir

“…Nevertheless, the simultaneous action of internal and external factors forms a combined cause. The identification and evaluation of low resistivity in the reservoir, which is an important issue in the field of logging [2,[7][8][9][10], have always been difficult. This is because the generation mechanism of low resistivity is complex and it differs in various oilfields, which introduces great difficulty to the interpretation of well logging data in every particular area [11][12][13][14][15][16].…”