PROBLEMS OF OIL-GAS-CONDENSATE FIELD AT THE LATE STAGE OF EXPLOITATION

V.A. Istomin (NOVATEK JSC, Moscow, ) G.A.Lanchakov, V.A Stavitskiy, N.A.Tsvetkov ( dobycha Urengoy LLC, Novy Urengoy, Russia)

Urengoy Oil-Gas-Condensate field on the primary proven deposits exceeds 12 tcm of gas. The field is situated in the Western Siberia on the North of the region in the areas of unstable permafrost, with the severe climate conditions and with the total absence of infrastructure at the beginning of its development. Basic features of Urengoy field: - multilayer productive horizons (from the bearing Senomanian horizons to Achimov and Jura sediments) - considerable distinctive gas-condensate characteristics of the productive horizons (from practically total condensate lack in Senomanian deposits to 300-400 g/m3 of hydrocarbon condensate in Achimov deposits) - the presence of the considerable ethane content up to 5-7 mol. % in natural gas (that determines the future of gas-chemistry development in the region) - the presence of the formation anomalous pressure factor (FAPF) (so anomalous factor in Achimov stratum is 2 and over, primary formation pressure reaches 70 MPa) in some deposits - the presence of oil rims in some gas-condensate deposits. As a result exploitation objects (5-6 objects) are distinguished with greatly distinctive primary formation pressure and gas-condensate characteristics as well as oil deposits (rims), which development has a considerable peculiarity in comparison with the ordinary oil deposits. Urengoy oil-gas-condensate field is developed since 1978. In the beginning Senomanian gas deposit had been developed, then Valanginian gas-condensate deposits were put into operation, Achimov deposits are being developing now. It is significant to note that the deepest bearing layers are not enough explored, that is why exploration drilling (including ultradeep drilling) is carried out. Gas conditioning technology of Senomanian deposits includes glycol gas dehydration, and the variations of low-temperature separation are used in gas treatment technology of Valanginian deposits. At present, Urengoy field is at the late stage of exploitation (concerning Senomanian and Valanginian deposits). In the report the results of thirty-year field exploitation are summarized. Basic technological exploitation problems are analyzed concerning both bearing layers and technological system – productive layer, well bottom zone, wells, gas gathering field pipelines and gas treatment facilities. The basic exploration directions and the results of technological works with the aim of effective problem solving in the course of field exploitation are presented in the report. By the practical realization of all suggested technological decisions, the special emphasis was paid to ecological aspects and an important task of the environmental risk minimization. Other principals of technical problem solving are connected with optimization of energy expense and exploitation cost reduction on gas and gas-condensate production.

The following original technologies are proposed on Senomanian deposits: - water shutoff of the wells and critical area of formation (with the aim of well sand and water seepage limitation) - production stimulation with the aim of stable inflow (fracturing etc.) - two stage gas glycol dehydration technology for providing of required gas quality characteristics and optimal technological equipment load - automatization of gas cooling apparatus for optimal gas temperature and for effective preventing gas hydrates in the cooling apparatus pipes.

The following original technologies are proposed on Valanginian deposits: - gathering field pipelines with two different pressure levels for increasing of Valanginian wells output

- optimization of loss C5+ from the low-temperature separators - combined technological schemes of Valanginian and Senomanian gases treatments with the optimal usage of the booster compressor system - recycling technologies for preventing gas hydrates with the usage of methanol as a thermodynamical inhibitor (including its usage by boosters at the top of the technological process) - special range forming for waste burial and monitoring of the ecological safety of pump-down of industrial wastewaters.

The above technical decisions are protected by some RF patents (more than 20 patents) and their introducing gave considerable economic efficiency. Applying of these technological decisions allowed optimizing gas-gathering and field gas treatment processes, reducing the exploitation cost and providing effective gas and condensate recovery at the late stage of Urengoy oil-gas-condensate complex development.