Condensate Recovery By Cycling At Declining Pressure

Appreciable liquid and gas reserves can be found in gas condensate reservoirs. During gas production from the gas condensate reservoirs, the bottom-hole pressure may drop below the dew point pressure. When this occurs, liquid condensate will start to drop out of gas phase and accumulate in the area close to the wellbore where the pressure drop will be maximum. The accumulation of condensate, and sometimes water, in the area around the wellbore will result in reduction in the gas permeability and hence loss of production of gas and liquid condensate. Several techniques have been used to mitigate the problem of condensate and liquid blockage (banking) in gas reservoirs. These methods include injection of low flash point solvents, wettability alteration surfactants, gas cycling and hydraulic fracturing. None of the state of the art is a panacea for the problem since each method has its own pros and cons. In the current study, a novel chemical treatment formulation based on surface modified fluorinated silica nanoparticles (NP) was developed to mitigate the problem of condensate and water banking. The newly developed formulation is able to effectively alter the wettability of the rock surface from oil and/or water wetting to neutral wettability for both phases or to intermediate gas wet. The size distributions of the fluorinated silica nanoparticles were characterized by dynamic light scattering (DLS). The contact angle of water and decane on the new formulation-treated rock surfaces was measured to characterize wettability alteration of the treatment. Coreflood experiments were performed using outcrop samples and field gas condensate fluid composition under reservoir conditions (temperature is 300°F and pressure is 4000 psi). To investigate the nanoparticle size effects, two batches of the fluorinated silica nanoparticles with average sizes of 135, 180 and 400 nm were synthesized. The contact angle measured of water and decane on the treated sandstone surface was found to be 120 and 51 degrees, respectively; indicating that the fluorinated nanoparticles were able to change the wettability of the rock surface to strongly non-water wetting and moderately decane wetting. Several coreflood experiments were performed to optimize the fluorinated nanoparticles concentration and the solvent package. It was revealed that only three pore volumes (PV) of a treatment formulation composed of 0.065 wt.% concentration of fluorinated nanoparticles in butanol were able to achieve 37% improvement for gas and liquid relative permeability. The new fluorinated nanoparticle-based treatment reported herein was able to change the rock surface wettability to be non-wetting with liquids (both water and decane) or intermediate gas wetting effectively. More importantly, the treated surface was relatively long-lasting since the pressure drop after treatment was shown to be fluctuating around 33 to 36 psi (the same level after pumping 250 pore volumes of gas condensate mixture from our lab experiments under reservoir conditions.

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Comparative Evaluation of Gas-Condensate Enhanced Recovery Methods for Deep Ukrainian Reservoirs: Synthetic Case Study

Burachok

Kondrat

Matkivskyi³

et al. 2021

SPE Europec Featured at 82nd EAGE Conference and Exhibition

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Low value of final condensate recoveries achieved under natural depletion require implementation of enhanced gas recovery (EGR) methods to be implemented for the efficient development of gas-condensate reservoirs. The study was performed using synthetic numerical 9-component compositional simulation model that approximated the typical conditions of deep gas-condensate reservoirs of Dnieper-Donetsk Basin in Easter Ukraine. Injection of water, methane, nitrogen, carbon dioxide, mixture of methane and nitrogen, mixture of methane, ethane and propane at different concentrations were evaluated at 50% and 100% voidage replacement for reservoir fluids with 100 g/m3, 300 g/m3 and 500g/m3 potential condensate yield. Condensate recovery studied at different stages after primary depletion, when reservoir pressure reached 25, 50, 75% from dew point and at pressure of maximum liquid dropout. Results comparison was done based on the two criteria: technical efficiency – incremental condensate recovery towards the base depletion cases and economic efficiency – cumulative NPV. Status of initial depletion as well as voidage replacement have a direct impact on breakthrough time and negative economic indicators. Despite providing the highest incremental condensate recovery by injecting CO2 at 100% voidage, it has a strong negative economic effect. Based on incremental condensate recovery EGR methods are ranked as following for all condensate potential yields and levels of primary depletion: CO2 100%; solvent gas mixture of C1 90%, C2 5%, C3 5%; solvent gas mixture C1 98%, C2 1%, C3 1%; C1 100%; mixture of C1 50% and N2 50%; N2 100%; water. Economically, the highest efficiency was shown for C1 100% injection, due to the fact, that produced re-cycled gas has a sales value as well. For the maximum incremental recovery it is advisable to start the injection as early as possible, while highest economic increments received for the cases of delayed injection, particularly when the reservoir pressure is equal to the pressure of maximum liquid condensation. The results of study can be used a guidance for rapid screening of applicable EGR method for gas-condensate fields depending on depletion stage and potential condensate yield.

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Condensate Recovery By Cycling At Declining Pressure

Cited by 3 publications

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A Safer Generation of Wettability Alteration Chemical Treatments

A Safer Generation of Wettability Alteration Chemical Treatments

Novel Surface Modified Nanoparticles for Mitigation of Condensate and Water Blockage in Gas Reservoirs

Comparative Evaluation of Gas-Condensate Enhanced Recovery Methods for Deep Ukrainian Reservoirs: Synthetic Case Study

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