Gazovaya promyshlennost’ № 08 2021

For the fields of Uzbekistan, whose development is either complete or at the late stage, with gas deposits confined to terrigenous reservoirs, the gas recovery factor varies from 0.50 to 1.00 with an average of 0.64. Such a scatter allows us to conclude that some hydrocarbon reserves are underestimated, whereas others are overestimated. The gas recovery of terrigenous pay reservoirs developed in the natural (gas) mode depends mainly on the determination of hydrocarbons initially-in-place, field development system efficiency, lithological characteristics of the reservoirs, pore space structure peculiarities along the area and section of the pay horizons, their thickness persistence, and the homogeneity of their interlayers. Given these factors, we have examined the ultimate gas recovery of deposits across the Sudochy deflection fields (Republic of Karakalpakstan, West Uzbekistan). The reserves were estimated by the pressure-drop method, and the criteria were the volume of gas initially-in-place involved in drainage and how it changed during operation. Causes analysis for obtaining specific ultimate gas recovery values (g) allowed us to divide all the considered fields into four groups: А (g = 0.80–0.95); В (g = 0.70–0.80); С (g = 0.60–0.70); D (g = 0.50–0.60). The study results show that the forecast gas recovery factors are mainly close to those actually achieved, so they can be used to predict gas recovery factors of terrigenous reservoirs.

The paper describes the methods of studying gas reservoirs based on the detailing the geological-field model into layers and monitoring the movement of the gas-water contact while controlling the development. The characteristic features of the layers’ identification in the Cenomanian deposits’ section, methods, criteria, and procedures for the layers’ correlation using original tools, tested in many fields in the southern part of the Nadym-Purskaya oil and gas area (Vyngapur, Komsomolskoye, West Tarko-Sale, Ety-Pur, Vyngayakha, Gubkinskoye fields) are presented. There are shown the features of the construction of the reservoir roof surface and the initial gas-water contact, which allow us to form a reasonable geometry of the geological-field model. As a result of layers’ identification, it is possible to detail the reservoir structure by filtration characteristics, dynamics of reservoir pressure drop and explain many problems of wells’ watering and variability of development parameters during operation. The main difficulties in assessing the current gas-water contact in gas wells are identified, and methods for its determination in operation mode, based on experience, are proposed. Original methodology of calculation the quarterly values of gas-water contact lift with its measurements allows to reasonably develop maps for selected dates and conduct detailed monitoring on the reservoir using CTC-EXPERT tools (OOO COMTECO (limited liability company)). Considerable attention is paid to graphical representation of the results of layered structure formation (layer boundaries, faults), observations of contact movement and elements used in operation (wells, perforation) when controlling the development. The main examples of the influence of the layered model structure features on the dynamics of operation parameters and the model of contact movement are described.