Effects of Dolomitization on Porosity during Various Sedimentation-Diagenesis Processes in Carbonate Reservoirs

Abstract

Carbonate reservoirs, especially dolomite reservoirs, contain large reserves of oil and gas. The complex diagenesis is quite challenging to document the dolomite reservoirs formation and evolution mechanism. Porosity development and evolution in dolomite reservoirs primarily reflect the comprehensive effect of mineral dissolution/precipitation during dolomitization. In this study, multicomponent multiphase flow and solute transport simulation was employed to investigate dolomitization in the deep carbonate strata of the Tarim Basin, Northwest China, where active exploration is currently under way. One- and two-dimensional numerical models with various temperatures, fluid compositions and hydrodynamic characteristics were established to quantificationally study dolomitization and its effect on porosity. After determining the main control factors, detailed petrologic characteristics in the studied area were also analyzed to establish four corresponding diagenetic numerical models under different sedimentary environments. These models enabled a systematic analysis of mineral dissolution/precipitation and a quantitative recovery of porosity evolution during various sedimentation-diagenesis processes. The results allowed for a quantitative evaluation and prediction of reservoir porosity, which would provide a basis for further oil and gas exploration in deep carbonate reservoirs.

Geometric and Fractal Characterization of Pore Systems in the Upper Triassic Dolomites Based on Image Processing Techniques (Example from Žumberak Mts, NW Croatia)

“…The porosity of early diagenetic dolomites from Samoborsko gorje and Medvednica Mts (a few km east from our research area) ranges from 0.92 to 2.21% [74], correlating with our results. The porosity decrease due to diagenesis in Tarim Basin (NW China) is up to 40%, with final porosity values from 4.2 to 18.2% [75].…”

Coupling Relationship between Multistage Fluid Activity and Reservoir Abnormally High-Porosity Zones in the Songtao–Baodao Region, Qiongdongnan Basin

“…It is noteworthy that the CO 2 content of the gas reservoirs in the third AHPZ in the Baodao 19-B belt is as high as 81.6%~87.9%. The carbon isotope value of CO 2 ranges from −7.5‰ to −6.9‰, with a 3 He/ 4 He value of 5:95 × 10 −6 -8:75 × 10 −6 , and an R/Ra ratio of 4.25-6.25 [26], which indicates an inorganic mantle CO 2 source [43], and may be related to the Miocene volcanic activity close to the No. 2 fault structure (Figure 1(d)).…”

“…For example, sandbody that contains high content of rigid particles, few argillaceous impurities, and coarser grain generally has a strong resistance to compaction during burial, thereby preserving more pores at the same burial depth. The cementation is generally weak in the middle of thick sandbody, and the pore is relatively well preserved [4]. Grain coat grows outward from the surface of skeleton grains.…”

“…Reservoir Diagenetic Fluid Type and Evolution. In addition to its own properties, reservoir diagenetic fluid in the sedimentary basin is affected by external factors, including meteoric water, organic and carbonic acids, and thermal and hydrocarbon fluids[3,4]. The property variations of diagenetic fluids in different geological periods have a large influence on the products of reaction between fluids and…”

Reactive Flow in Carbonate Rocks From Lacustrine Environments: The Effects of Pressure and Fluid Salinity

“…Moreover, Mg silicates, such as clay minerals, also influence the porosity evaluation due to the dissolution of these clay minerals. The conditions of the reservoir, such as temperature, pressure, and mineral species, play a critical role in the porosity evolution during diagenesis (Yang et al 2020;Wright, 2020).…”