Characteristics Of The Formation Water And The Corresponding Exploitation Strategy For Area â…¡ In Southern Ma5₁ Reservoir In Jingbian Gas Field

In view of that formation water in the marine carbonate reservoir in western-China basins has a complicated distribution, for each reservoir presents a special occurrence of formation water, the Lower Paleozoic Ma5₁ accumulation was taken as a case to study and search the theory and methodology for analysing the formation water in such gently inclined and fossil-karst-trap dominant strata so as to reveal origin sof the formation water, to recognize the regular pattern of gas-water distribution, to predicate and evaluate new oil-gas accumulation zones and to rationally exploit the water-containing gas pools. Basing on the studies of former researchers on Ma5₁ reservoir the thesis analyzed the water-producing mechanism for water-producing wells, carried out evaluation of the distribution of relatively water-rich areas, and had a gas reservoir engineering analysis for the dynamic state of southern II areas wells, and proposed an exploitation strategy in view of the distribution of water-rich areas. Basing on the geological and exploitation data available, geology, logging and numerical simulation were integrated and static analysis and dynamic prediction combined in this study, which led the following results.(1) Logging features of reservoir in the studied area were analyzed systematically. In combination with the well testing and water analysis information, cross plot and multivariate recognition were employed, to discriminate formation fluid. By integrating geological, seismic and dynamic-state data, the distribution of relative water-rich areas has been revealed.(2) Types and characteristics of the formation water were studied, including the analysis of sources and evolution of the water, vertical and lateral correlation of the aquifer beds, recognition of the distribution of relative water-rich areas and the relevant causes. It is thought that owing to the structural reversion and gentle inclination, the "energy" for gas migration is relatively insufficient which leads to an excessive residual water saturation and more or less formation water is producing from the gas wells, this is one of the main water-producing features in Ma5₁ reservoir in Jingbian gas field. The distribution of "relative water-rich areas" is controlled by such factors as regional tectonics, reservoir heterogeneity, local low-amplitude structure, sealing by reservoir alteration zone and so on.(3) Dynamic state of the water-producing wells, dynamic-state law for each gas-producing well and influence of water to the productivity of gas wells in Southern II area have been analyzed, the Mckette-Wehe alignment chart for calculating water content in gas been simulated, and the Turner formula for theoretically calculating the critical velocity of liquid-carrying flow in gas wells has been analyzed and the corresponding program and calculation have been worked out. Basing on the above-mentioned studies and combined with geologic recognition, the mechanism of water-output form water wells was analyzed, and the exploitation reserve in water-rich areas has been checked and re-evaluated.(4) By the geological analysis and numerical simulation, an exploitation strategy for water-rich areas was proposed accordingly. It is thought that the present well-network seems to be incomplete. It is reasonable to add development wells to the relatively well-scarce south-east and northern part of the studied area, which would enhance the well-completeness of these parts.