No abstract

Summary The ability of foam to divert gas flow during a long period of gas injection in a surfactant-alternating-gas (SAG) foam process is important for the economics of foam-diversion processes for enhanced oil recovery (EOR). Here, we interpret field data from the foam test in the Cusiana field in Colombia (Ocampo et al. 2013). In this test, surfactant was injected into a single layer that had been taking approximately half the injected gas before the test; then, gas injection resumed into all layers. On the basis of the size of the surfactant slug injected and estimates of adsorption and of water saturation in the foam in situ, we estimate that the treated region extended approximately 5.3 m from the injection well; fortunately, the results to follow are not sensitive to this estimate. On the basis of the change in injection logs before the test and at Day 5 of the test, when approximately 30 pore volumes (PVs) of gas (relative to the volume of the treated zone) had been injected, foam still reduced gas mobility in the treated layer to approximately 11% of its pretrial value. We base this estimate on the decrease of injection into the treated layer and the increase of injection into the other layers; the results are consistent among the layers. After 35 and 152 days of injection (220 and 1,250 treatment PV of gas injected), foam reduced gas mobility in the treated zone to approximately 26 and 50% of its value before the test, respectively. This result indicates that foam continued to reduce mobility by a modest amount even after long injection of gas. On the other hand, foam did weaken progressively as it dried out. Foam models in which foam remains strong at irreducible water saturation would greatly overestimate foam effectiveness at long times in this test. In this test, the large volume of gas had quickly penetrated far beyond the edge of the surfactant bank. Mobility in the foam-treated region in this test, after passage of many treatment PVs of gas injection, mimics that very near the injection well in a process with a larger slug of surfactant.

A successful field trial of foams as gas injection conformance enhancer has been deployed in the Cusiana field in Colombia, South America. This work describes the Front End Loading (FEL) process done to get to the field trial, the field operation itself, and the results obtained so far. The Foam treatment was deployed in the Mirador formation of the Cusiana field, a low porosity quartzarenite with a recovery factor over 50%.The reservoir fluid is a volatile oil developed under an extensive gas reinjection process. The foam treatment was engineered to improve both the gas injection conformance at the wellbore and also the gas sweep efficiency deep into the reservoir. An extensive FEL including chemical product screening, foam stability at reservoir conditions, coreflood experiments, reservoir modelling, and a careful selection of well candidates was executed for this pilot. The treatment was done in a gas injector well in the northern part of the field, where high RF has already been obtained with high levels of gas recycling. The operation was performed using the SAG method. The foaming surfactant was pumped selectively in front of the dominant injection layer and then the well was put back on injection. The results showed a clear and sustained change in GI conformance reducing the injectivity of the treated layer by 60%. Increase in oil rate along with decreases in GOR was also observed in the nearby oil producers two months after the treatment. Results herein presented confirm the viability of foams as an EOR method for the Cusiana field and at least two other fields located in the same basin and exploited under similar conditions. Introduction The Cusiana field currently operated by Equion Energía Ltd is located in the foothills of the Eastern Mountain chain in Colombia - South America, and started production in 1994. It comprises three stacked reservoirs (Mirador, Barco and Guadalupe) and two compositional fluid systems both being volatile oils with a rich gas cap near critical conditions with pressures and temperatures over 5000 Psia and 250 F respectively (Lee et al, 1996). Initial fluids in place added up to about 1.5 bn STB of oil and over 3 tcf of gas with Mirador formation bearing about 60% of total fluids. Development strategies have included natural depletion, gas recycling, water injection and gas injection redistribution. Gas recycling and re-distribution have provided the best recoveries so far.

The ability of foam to divert gas flow over a long period of gas injection in a Surfactant Alternating Gas (SAG) foam process is important for the economics of foam-diversion processes for enhanced oil recovery. Here we interpret field data from the foam test in the Cusiana field in Colombia, South America (Ocampo et al., 2013). In this test surfactant was injected into a single layer that had been taking about half the injected gas before the test; then gas injection resumed into all layers. Based on the size of the surfactant slug injected and estimates of adsorption and of water saturation in the foam in situ, we estimate that the treated region extended about 5.3 m from the injection well: fortunately the results to follow are not sensitive to this estimate. Based on the change in injection logs before the test and at day 5 of the test, when approximately 30 pore volumes of gas has been injected, foam still reduced gas mobility in the treated layer by about a factor of 9. We base this estimate on the decrease of injection into the treated layer and the increase into the other layers; the results are consistent among the layers. After 35 and 152 days of injection (220 and 1250 pore volumes gas injected), foam reduced gas mobility in the treated zone by about a factor of 4 and 2, respectively. This result suggests that foam continued to reduce mobility by a modest amount even after long injection of gas. In this test, the large volume of gas had quickly penetrated far beyond the edge of the surfactant bank. In a design where a larger bank of surfactant were injected, a much greater and longer diversion of gas would be expected. On the other hand, foam did weaken progressively as it dried out. Foam models where foam remains strong at irreducible water saturation would greatly overestimate foam effectiveness at long times in this test.

This paper presents the development and successful implementation of the Foams technology as an effective EOR mechanism to improve the sweep efficiency of the gas injection in the Piedemonte fields. It also shows the process of optimization of the technology to adapt it to the Piedemonte operating conditions, which is based on massive hydrocarbon gas reinjection, and how this process led us to be at a state of the art position in this technology. The methodology to adapt and further develop the foam EOR technology in Piedemonte was based on the Capital Value Process (CVP). It starts with a screening exercise, passes through a technical assurance including applicability, fluids compatibility, modeling and coreflooding tests at reservoir conditions. Finally, the specific solution is implemented in the field to confirm effectiveness. Initially the foams were deployed using the conventional Surfactant Alternating Gas (SAG) technique, but then the technology was optimized to better suit the operating conditions of the fields, and the last interventions have been done dispersing the foamer chemical in the gas stream. This technology has been implemented in most of the fields in the Piedemonte and has proved success since the early implementation pilots in 2011. Implementation started in the Cusiana field, which is a matrix dominated system, and then moved to the naturally fractured and low porosity reservoirs located in the Recetor and Floreña fields. In all the cases, the implementation of foams has rendered positive results reflected in incremental oil production and flattening of the Gas Oil Ratio (GOR) at the influenced producer wells. The new developed dispersed Foams technology has been as effective as the conventional SAG in the jobs performed so far, with the advantages of requiring less surface equipment, and water consumption than SAG jobs. Benefits from Foams implementations so far add up to about 0.65 MM STB. Main conclusions from this project are i) The foams EOR technology is fully applicable in the Piedemonte fields to improve the gas sweep efficiency and increase final oil recovery. ii) A new foam deployment technique based on the injection of the foamer chemical dispersed in the gas stream was developed, and proved effectiveness at the field. The work is innovative in two ways: i) Effectiveness of foam as a technology to improve gas sweep efficiency in naturally fractured dominated systems was proved. ii) A new foam deployment technique based on the injection of the foamer chemical dispersed in a non-condensable gas stream was developed. Also this new foam EOR technique can be extrapolated to any other field operated under gas injection.