Substantiation of the petrophysical properties of complex-structured carbonate reservoirs in the Bukhara-Khiva oil and gas region: A case study of the Alan field

Abstract

This study investigates the petrophysical properties of complex carbonate reservoirs in the Alan field, Chorjou step, Bukhara-Khiva oil and gas region, to support spatial distribution and reserve estimation. It aims to identify factors driving the "apparent saturation" effect and low-resistivity pay zones in the Jurassic carbonate sequence (horizons XV-HP, XV-P, XV-ΠΡ, and XV-a), using well logging data (Gamma Ray, Resistivity, Neutron, Sonic) and core analysis linking porosity, permeability, clay content, and fracturing. Results reveal extreme heterogeneity and a bimodal porosity system. Despite relatively uniform total porosity (12–18%) across horizons, permeability and water saturation differ drastically: the upper reef horizons (XV-HP, XV-P) show high permeability (285–400 mD) and low water saturation (11–13%) from vuggy, fractured structures, while the lower sub-reef and basal horizons show reduced permeability (~11.6 mD) and saturation up to 35%. This disparity stems from diagenetic clay minerals (montmorillonite and kaolinite) and isolated micropores, which raise capillary forces and cation exchange capacity, suppressing resistivity and creating an apparent high-saturation effect. Conventional interpretation is insufficient for such systems; integrating Digital Rock Physics and artificial intelligence is recommended to differentiate low-resistivity pay zones, reduce geological uncertainty, and optimize field development, thereby preventing early water breakthrough and maximizing recovery efficiency.

English abstract as published with the paper (CC BY 4.0). The authors’ abstract, reproduced under CC BY 4.0.

In plain English

O. Karshiyev, I. Holmurodov and O. Bolibekov of the Institute of Geology and Exploration of Oil and Gas Fields (IGIRNIGM) study the petrophysical properties of the complex carbonate reservoirs of the Alan field on the Chorjou (Chardzhou) step of the Bukhara–Khiva oil and gas region, to support mapping of the reservoirs and reserve estimates. They look for the causes of an “apparent saturation” effect and of low-resistivity pay zones in four horizons of the Jurassic carbonate sequence, XV-HP, XV-P, XV-ΠΡ and XV-a, using gamma-ray, resistivity, neutron and sonic logs and core analyses that link porosity, permeability, clay content and fracturing.

The reservoirs are very heterogeneous, with a bimodal pore system. Total porosity is fairly uniform at 12–18% across the horizons, but permeability and water saturation differ sharply. The upper reef horizons, XV-HP and XV-P, have vuggy, fractured rock with permeability of 285–400 mD and water saturation of 11–13%. The lower sub-reef and basal horizons have permeability of about 11.6 mD and water saturation of up to 35%. Diagenetic clay minerals, montmorillonite and kaolinite, and isolated micropores raise capillary forces and cation exchange capacity; this lowers resistivity and makes the rock look more water-saturated than it is.

The authors conclude that conventional log interpretation is not enough for such rocks. They recommend digital rock physics and artificial intelligence to pick out low-resistivity pay zones, reduce geological uncertainty, prevent early water breakthrough and raise recovery. The structure and reservoirs of the Bukhara and Chardzhou steps are also described in Ulmishek (2004).

How to cite

O. Karshiyev, I. Holmurodov and O. Bolibekov (2026). Substantiation of the petrophysical properties of complex-structured carbonate reservoirs in the Bukhara-Khiva oil and gas region: A case study of the Alan field. E3S Web of Conferences, vol. 745, 06001. https://doi.org/10.1051/e3sconf/202674506001