Graduate Seminar

Mork Family Department of Chemical Engineering and Materials Science
Graduate Seminar“Integration of Laboratory, Modeling and Field Studies to Evaluate a Waterflooded Vuggy Carbonate Reservoir for Application of Improved Oil Recovery Methodsâ€ÂDr. Kaveh Dehghani
ChevronAbstract A waterflooded vuggy carbonate reservoir in Permian Basin was considered for application of Improved Oil Recovery (IOR) methods. An integrated laboratory, modeling and field study was used for the evaluation process. The following shows different parts of the evaluation process: A methodology was developed to model and successfully history match the primary and waterflood phases in a 15 well, 100 acre vuggy portion of the field. This method is based on a derived log trace of secondary porosity calculated by subtracting sonic porosity (matrix only) from a core calibrated total porosity transformed from Density and Neutron-logs. Log signatures of vugular intervals were developed recognizing significant differences in matrix and total porosity. A detailed geostatistical distribution of total porosity was first generated and permeability was assigned using a cloud transform of core data from nearby wells. Two geostatistical distributions of secondary porosity with different correlation lengths were then generated using the developed secondary porosity trace. Vugular zones were assumed to have a secondary porosity of 8% or greater. These models were superimposed on the permeability cube by assigning exceptional high permeability values to the vuggy zones. Using a general scale up method, the detailed permeability cubes were scaled-up for simulation studies. The models incorporating vuggy permeability distributions showed a far superior history match of primary and waterflood performance than those without vuggy permeability distributions. Good history match was also obtained on individual well basis. Sensitivity of the match to vuggy zone permeability and correlation length was analyzed. Results from these simulation runs provide insight into the spatial distribution and permeabilities of the vuggy zones. During the process of this examination it was recognized that this reservoir was a potential candidate for the steam injection process. Thin zones of vuggy high porosity and high permeability within the main pay interval have threatened the effectiveness of waterflood, leaving a major portion of oil by-passed in the lower permeability matrix. Feasibility of increasing recovery by steam injection in this part of the field was investigated using thermal compositional models. The analysis of the results from this modeling practice showed that primary recovery produced 14% of OOIP and waterflood added a 12% incremental recovery. The results also showed that combining a short steamflood cycle followed by a blow-down cycle from all wells (including the injectors) resulted in a big kick in both oil production rate and cumulative oil production curves (e.g., 2.5 years of flood followed by 2.5 years of production). The best scenario of well configuration was 10 acre 5 spots with incremental oil recovery of 18% of OOIP. A preliminary economic calculation showed steam injection to be economically feasible. We also conducted laboratory experiments on a core sample from this reservoir in order to quantify the recovery mechanisms. These comprise thermal expansion, thermally enhanced solution gas drive, vaporization, and in-situ steam drive. Computed Tomography (CT) imaging of a miscible flood was used to characterize the connectivity of the vugs and matrix rock. A series of blow-down tests were then conducted by heating the core to 300 â—‹ F. The backpressure regulator on the system was set just above the bubble point of the oil at 300 â—‹ F. The pore pressure was then reduced at a constant rate from one end of the core sample. The first blow-down test was with the core at initial oil saturation with pressure reduction from the top of the sample; the second at initial oil saturation with pressure reduction from the bottom; and the third at residual oil saturation to water with pressure reduction from the top. The volumes and compositions of the produced fluids were measured in all the blow-down tests. The initial and final oil saturation distribution for the second blow-down experiment was also CT imaged. The CT images reveal that the core sample contains vugs, high permeability matrix, and low permeability matrix rock; and that the vugs are connected through the high permeability matrix. The blow-down experiments show that 50-68% of the oil is recovered; with 8-20% due to thermal expansion, 20-24% due to thermally enhanced solution gas drive, 12-16% due to dry distillation, and 8-10% due to in-situ steam drive.Friday, October 28, 2005
Refreshments at 1:30 p.m. â€" HED Lobby
Seminar at 1:45 p.m.
HED 116
The Scientific Community is Cordially Invited

Location: Hedco Pertroleum and Chemical Engineering Building (HED) - 116

Audiences: Everyone Is Invited

Contact: Petra Pearce