Experimental modelling of a recovery technique for liquid hydrocarbons at saturations lower than the flow threshold from gas-saturated deposits of gas-condensate and oilgas- condensate fields

This paper presents the results of experimental modelling of a recovery technique for hydrodynamically immobile liquid hydrocarbons (LHC — oil and retrograde condensate) from productive formations of gas-condensate and oil-gas-condensate fields (GCFs and OGCFs) — on the example of the main deposit of Vuktyl OGCF. The technique is based on cyclic injection of hydrocarbon solvent and dry gas, with further recovery of remaining LHC and solvent by dry gas or dry gas with slugs of propane-butane fraction. Experiments on core models showed high potential technological efficiency — recovery factors (displacement efficiency) up to 0.72 for LHC and 0.99 for the solvent. In combination with developed infrastructure and low current reservoir pressures, these results indicate possible achievement of profitability of LHC recovery with this technique at Vuktyl OGCF and other GCFs and OGCFs at late development stages, as well as usefulness of further modelling and pilot field studies.

Materials and methods

Experimental modelling, chromatography, reservoir core model, recombined model of reservoir HC fluids (reservoir oil, gas-condensate system), hydrocarbon solvent, methane, propane-butane fraction.

Results

This paper presents the results of the experimental studies on core reservoir models on the techniques for recovery of hydrodynamically immobile LHCs (reservoir oil and retrograde condensate) from gas-saturated productive deposits of the Vuktyl OGCF. To achieve this goal, the following main tasks were solved during the research:

— an experimental setup was assembled for physical modeling of the process of LHCs recovery on core models under reservoir conditions with chromatographic analysis of the output production (liquid and gas phases);

— an experimental modeling program for LHC-production techniques from gas-saturated productive deposits of the Vuktyl OGCF;

— in the core model of the reservoir, the component composition, thermobaric and phase state of the reservoir oil-gas-condensate system were reproduced, including the connate water and LHCs (oil and retrograde condensate), adequate to the main reservoir of the Vuktyl OGCF at current development stage

— experimental modeling of recovery of hydrodynamically immobile LHCs was carried out by cyclic injection of hydrocarbon solvent, easily evaporated under reservoir conditions, and dry gas with the final injection of dry gas and its mixture with the propane-butane fraction to maximize solvent recovery and return it to the LHC-recovery process;

— to determine the efficiency of the technology, a quantitative assessment has been made for the dynamics of recovery factors for LHCs and hydrocarbon solvent injected into the reservoir (reservoir model).

Conclusions

For the first time, based on physical modeling, the recovery technique for hydrodynamically immobile LHCs (reservoir oil and retrograde condensate) from the gas part of carbonate deposits of oil-gas-condensate fields at the final stage of their development was experimentally investigated on core reservoir models.

The obtained experimental results allow to recommend this technique for further technical and economic assessment and conducting pilot field studies as a method for LHC recovery and increasing component recovery factors in relation to deposits of the Vuktyl OGCF at the current stage of its exploitation.

The potential for cost-effective implementation of this LHC-recovery technology at the late stages of OCCFs development is associated with:

— well-equipped and developed infrastructure of the fields at this period;

— low reservoir pressures, providing close to maximum accumulated volumes of retrograde condensate in the reservoir LHCs, and therefore LHC saturation approaching the flow threshold in productive gas-saturated reservoirs.

To reduce the cost of the technology implementation, it is necessary to ensure effective recovery of the solvent from the produced raw fluid and its return to the process of LHC recovery.