Patent EA-004752-B1 (EA)
Title: Determining the in situ effective mobility and the effective permeability of a formation
Inventor: HASHEM MOHAMED NAGUIB
IPC: E21B49/08
Filed: 2002-01-17
Abstract: 1. Method of determining the in situ effective mobility of a formation layer traversed by a borehole, which method comprises the steps of: a) selecting a set of locations in the formation layer; b) selecting from the set a first location; c) lowering in the borehole to the location a tool that comprises a central conduit having an inlet and being provided with a pressure sensor, a fluid receptacle having an inlet opening into the central conduit, a fluid analyser, and means for discharging fluid; d) making an exclusive fluid communication between the formation and the inlet of the central conduit; e) allowing formation fluid to pass through the central conduit, allowing the formation fluid to enter into the fluid receptacle, and measuring the pressure build-up; f) determining the mobility from the pressure build-up; g) positioning the tool near a next location and repeating steps d) through f) until the mobilities of the locations in the set have been determined; h) determining for one location of the set the effective mobility, calculating the permeability for this location using the known viscosity of the uncontaminated formation fluid, and determining the viscosity of contaminated formation fluid using the permeability and the mobility determined in step f) for that location; and k) calculating the permeabilities for the other locations of the set using the viscosity of the contaminated formation fluid and the mobility determined in step f), and calculating the average of the permeabilities, wherein determining the effective mobility, which is the mobility of the formation with respect to the uncontaminated formation fluid, comprises the steps of: 1) selecting a location in the formation layer; 2) lowering in the borehole to the location a tool that comprises a central conduit having an inlet and being provided with a pressure sensor, a fluid receptacle having an inlet opening into the central conduit, a fluid analyser, and means for discharging fluid; 3) making an exclusive fluid communication between the formation and the inlet of the central conduit; 4) allowing formation fluid to pass through the central conduit, analysing the fluid, allowing the formation fluid to enter into the fluid receptacle when the fluid is the substantially uncontaminated formation fluid, and measuring the pressure build-up; and 5) determining the effective mobility from the pressure build-up. 2. The method according to claim 1, wherein making an exclusive fluid communication between the formation and the inlet of the central conduit comprises extending into the formation a probe having an outlet that is in direct fluid communication with the inlet of the central conduit of the tool. 3. The method according to claim 2, wherein making an exclusive fluid communication further includes activating a heating device arranged near the probe to heat the formation fluid. 4. The method according to claim 1, wherein the borehole is cased and wherein the steps a) through g) comprise the steps of: a1) making a plurality of perforation sets through the casing wall into the formation layer; b1) selecting a first perforation set; c1) lowering the tool into the borehole to the perforation set, which tool is further provided with an upper and a lower packer arranged at either side of the inlet of the central conduit, wherein the discharge opens below the lower packer, wherein the distance between the upper and the lower packer is larger than the height of a perforation set, and wherein the spacing between adjacent perforation sets is at least equal to the length of the longest packer; d1) setting the packers so that the perforation set is straddled between the packers; e1) allowing formation fluid to pass through the central conduit, allowing formation fluid to enter into the fluid receptacle, and measuring the pressure build-up; f1) determining the mobility from the pressure build-up; and g1) positioning the tool near the next perforation set, and repeating steps d1) through f1) until the mobilities of a predetermined number of locations have been determined. 5. The method according to any one of the claims 1-4, further including calculating along the formation layer the pressure gradient, and determining the viscosity from the pressure gradient using an empirical relation that had been obtained by fitting a curve through previously obtained data points comprising the measured viscosity as a function of the pressure gradient. 6. Method of taking a sample of uncontaminated formation fluid from a formation layer traversed by a borehole, which method comprises the steps of: a) selecting a set of locations in the formation layer; b) selecting from the set a first location; c) lowering in the borehole to the location a tool that comprises a central conduit having an inlet and being provided with a pressure sensor, a fluid receptacle having an inlet opening into the central conduit, a fluid analyser, and means for discharging fluid, which tool further comprises a sample container; d) making an exclusive fluid communication between the formation and the inlet of the central conduit; e) allowing formation fluid to pass through the central conduit, allowing the formation fluid to enter into the fluid receptacle, and measuring the pressure build-up; f) determining the mobility from the pressure build-up; g) positioning the tool near a next location and repeating steps d) through f) until the mobilities of the locations in the set have been determined; and h) selecting the location having the largest mobility as the location where a sample is taken. 7. The method according to claim 6, wherein making an exclusive fluid communication between the formation and the inlet of the central conduit comprises extending into the formation a probe having an outlet that is in direct fluid communication with the inlet of the central conduit of the tool. 8. The method according to claim 7, wherein making an exclusive fluid communication further includes activating a heating device arranged near the probe to heat the formation fluid. 9. The method according to claim 6, wherein the borehole is cased and wherein the steps a) through g) comprise the steps of: a1) making a plurality of perforation sets through the casing wall into the formation layer; b1) selecting a first perforation set; c1) lowering the tool into the borehole to the perforation set, which tool is further provided with an upper and a lower packer arranged at either side of the inlet of the central conduit, wherein the discharge opens below the lower packer, wherein the distance between the upper and the lower packer is larger than the height of a perforation set, and wherein the spacing between adjacent perforation sets is at least equal to the length of the longest packer; d1) setting the packers so that the perforation set is straddled between the packers: e1) allowing formation fluid to pass through the central conduit, allowing formation fluid to enter into the fluid receptacle, and measuring the pressure build-up; f1) determining the mobility from the pressure build-up; and g1) positioning the tool near the next perforation set, and repeating steps d1) through f1) until the mobilities of a predetermined number of locations have been determined. 10. The method according to any one of the claims 6-9, further comprising determining the effective mobility from the pressure build-up of substantially uncontaminated formation fluid.