Explaining the Reasons Why Well Deliverability of Off-Shore Gas and Gas Condensate Fields Is Declining

Vladimir I. Smurygin The State Unitary Enterprise of the Republic of Crimea Chernomorneftegaz Simferopol' vsmurygin@gas.crimea.ru
Ruslan U. Rabaev FGBOU VO Ufa State Petroleum Technological University Ufa rabaevru@rusoil.net
Bulat S. Muslimov FGBOU VO Ufa State Petroleum Technological University Ufa bmuslimov@mail.ru
Shamil Kh. Sultanov FGBOU VO Ufa State Petroleum Technological University; Institute of strategic researches of the Republic of Bashkortostan Ufa ssultanov@mail.ru
The articles postulates possible causes of decline in well productivity in development of gas and gas condensate reserves of the Black Sea off-shore fields. Quantification of the current energy related status of the formation, residual reserves and production capability of the wells as well as their interconnection has been made in the form of a system of equations characterizing the "formation - well" model.
Materials and methods
The holistic analysis of gas or gas condensate deposit development. Methods of statistically processing the production data.
The results yielded by the analysis of the pressure recovery curve for well No.1 registered between 2006 and 2009 go toshow that all the pressure recovery curves have been found to be noisy which, on the one hand, is attributable to the fact that wellhead pressures were registeredand, on the other hand, it can be put down to phase redistribution in the well bore after stoppage. Besides, areas of change in pressure derivate can be evidence of formation double porosity and were caused by pressure redistribution between the fracture network and the matrix.A steady trend for lower conductivity of the rock has been established. Formation pressure continues to be practically the same. Skin factor value close to zero is noted and absence of contamination in the bottomhole zone, too. In the extensive portion of the formation, one can observe reduced conductivity of the formation in respect of gas. Failure to achieve the planned rate of yield for gas as a result of commingling has resulted from damage caused by well killing fluids to production internals of the deposits in lower and upper Paleocene stratigraphic sequence of rocks and insufficiently effective development of wells after carrying out geotechnical interventions.
Results of re-interpreting the pressure recovery curves and well performance indicators show that the key reasons for reduced productivity of the wells are as follows: water encroachment of bed and sanding up of wells for reasons of sand carry-over caused by weakly cemented reservoir. The most probable cause of growing filtration resistance in wells is their self-kill with stratum water. When formation conductivity decreases, the condition of its bottomhole zone does not change. Hence, it can be concluded that it is the properties of the formation that change rather than its bottomhole zone. For purposes of a more in-depth study of the causes responsible for filtration resistance of the wells, it is recommended to conduct special geo-technical interventions and research.
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