Miscible gas flooding is the most commonly used enhanced oil recovery (EOR) method. One of the most important experimental parameters for miscible gas injection is minimum miscibility pressure (MMP). Many times, the MMP of a system can be very high. Instead of raising the pressure to achieve miscibility, injection gas may be enriched with intermediate components. The enrichment level at which the gas-oil system becomes miscible is called minimum miscibility enrichment (MME). Regardless of the values of MMP and MME, gas injected into a reservoir will most likely induce asphaltene precipitation, which may potentially cause formation damage and reduce flow in the production tubing. In this paper, reservoir fluid from a Kuwait reservoir was analyzed to check for the feasibility of miscible gas injection. First, a series experiments were conducted to measure MMP with various gases using different techniques and MME testing with slimtube experiments. Moreover, the benefits, disadvantages, and applicability of each experimental method for EOR testing with gas injections were compared. Second, asphaltene precipitation upon gas injection was investigated in detail by measuring the precipitation onset conditions. Asphaltene precipitation onset was measured using a near infrared (NIR) light-scattering technique and a high-pressure microscope system to analyze the measured data. Finally, the asphaltene precipitation locus on a pressure-temperature (PT) diagram and the amount of precipitation were modeled for the reservoir fluid with different concentrations of injection gas. The modeling was carried out using a composition-based cubic equation-of-state approach. The experimental and modeling results indicated that an increase in concentration of injection gas appears to aggravate asphaltene precipitation.
KOC undertook a major leap in its FDP expansion programme by a very comprehensive Miscible Gas EOR feasibility screening review of the North Kuwait (NK) Sabiriya and Raudhatain oil fields. This paper will highlight the major findings of the Phase 1 of this project executed in 2008. Phase 1 evaluated available resources and data required for implementation of an EOR Pilot followed by a full field implementation. Main emphasis was to evaluate EOR injectant supply options and identify a most-likely first source with the associated risks. The workscope encompassed 4 major task items: ▪Investigate and rank alternative injectants for technical/economic feasibility, recovery efficiency & local availability point of view:–CO2-the quality, quantity, usability from the industries, factories, power-plants.–Mixtures of CO2 & NGL from Jurassic Condensate–Feasibility of other methods such as water-alternating-gas (WAG) or nitrogen (N2) injection–Evaluate the Heavy Oil Project emissions as injectants.▪Review PVT EOR laboratory studies conducted by KOC to date. Screen data for consistency and representativeness for PVT/EOS modeling in Phase-2 sector/pattern reservoir simulation work. Characterize fluid property variation vertically and areally. Make recommendations.▪Review the completion and facilities for suitability in a CO2 & other injectant environment. Provide a first pass assessment of the associated gross economics to implement EOR scenarios that may require changes/uprgades to the surface facilities and/or completions.▪Review coreflood SCAL studies, solubility and miscibility tests including WAG. Compare waterflood and immiscible/miscible tertiary gasflood relative permeability experiments. Establish the need for carbonate rock leaching experiments for CO2 injection. Establish the need for asphaltene precipitation experiments for heavy API grades. The study identified pure CO2 and CO2/NGL mixtures as the most plausible miscible gas options worth pursuing a pilot study. For each Miscible Injectant type, the source options & supply volumes and the CAPEX and OPEX cost estimates were established. Semi- analytical recovery models were used to evaluate the EOR recovery efficiencies of the individual reservoirs, net injectant requirements and product streams. The detailed EOR cost model was built using the actual KOC well and facility cost Database and CAPEX and O&M costs for the industrial sourced CO2. A preliminary economics was performed using input from both models above. A pilot project to demonstrate the feasibility of CO2 WAG was also proposed.
Water injection is the most commonly used method for pressure maintenance in depletion drive reservoirs worldwide and there are numerous examples where the recovery has been enhanced significantly. However early breakthrough of injected water due to high permeability zones or thief zones mostly in heterogeneous carbonate reservoirs causes water recycling resulting in poor volumetric sweep and in turn adversely affects the oil recovery from the reservoir. A judicious mixture of proper reservoir management and development strategy may reduce the water recycling to a significant level. Sabiriyah Mauddud is a giant carbonate reservoir in North Kuwait and has been under production since last 57 years. Historical performance indicated very little aquifer support for the reservoir with no water production. A water flood pilot was initiated in 1997 when the reservoir had produced only 1% of its oil in place and pressure declined from its initial value of 3700 psi to the level of 2600 psi. Currently, the reservoir is under water flood with inverted 9 spot patterns in the crestal part and peripheral injection mainly in the western flank area. The water cut has gone up to the level of 42% after only low current oil recovery. High water cut is attributed to poor sweep efficiency due to preferential movement of water from conventional injector to producer through high permeability streaks/thief zones in the crestal area. As short term measure, a conformance plan to shut off the water contributing layers was prepared and has been introduced in the wells worked over during the period. Simulation run shows reduction in water cut by 5% by adopting the conformance plan. The new development strategy formulated for the field is to inject low and produce high from the reservoir and shifting the focus from crestal to peripheral injection. All the producers are planned to be completed with inflow control device to control the water production through the wells. The recently drilled producers are showing positive results and it is expected that the measures taken will help to maximize the benefits of water injection. The learning and the water flooding experience gained will be a valuable input for other reservoirs under water flooding.
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