Since 2015, Zarubezhneft JSC has been testing the steam-thermal effect on carbonate reservoir M saturated with native bitumen at the pilot area of Boca de Jaruco field (Republic of Cuba). Oil of deposit M is one of the heaviest in the world: viscosity in reservoir conditions is 36000 mPa·s, density is 1021.7 kg/m3. The reservoir rock is a fractured-porous carbonate with a dense fractures system. At the first stage of formation M development (2015-2019), the production was provided by vertical wells. During this time, commercial oil inflows were obtained: oil flow rates was up to 50 t/day, steam-oil ratio (SOR) reduced to 5 t/t during the best cycle. In 2020-2021 four horizontal wells were drilled as part of the second stage of pilot work. Horizontal wells are more efficient than vertical wells, primarily due to involved bituminous rocks volume increase. To implement this sweep, larger volumes of steam injection are required. Early 2021, due to the negative results of the first steam cycling stimulation (SCS) on horizontal wells, a decision was made to change the operation strategy. The new strategy was based on the principle of gradually increasing injection from smaller volumes to larger volumes (mini-SCS strategy). Since 2021 to present the achieved results of the pilot project confirmed the feasibility of choosing the mini-SCS strategy. From the first mini-cycles to the present, there has been a decrease in SOR for all horizontal wells; a record value of 4 t/t in the cycle has been reached. Based on the results obtained, an assessment of the prospects for horizontal wells during the period of business planning was implemented. Taking into account the presence of a dense system of fractures and small distances between wells (30-100 m), special attention is paid for monitoring and control of wells.
References
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