Patent EA-004669-B1 (EA)
Title: Determining the pvt properties of a hydrocarbon reservoir fluid
Inventor: HASHEM MOHAMED NAGUIIB
IPC: E21B49/08
Filed: 2002-01-17
Abstract: 1. A method of determining at least one of the in situ PVT properties of a hydrocarbon reservoir fluid that is present in a hydrocarbon-bearing formation layer traversed by a borehole, which method comprises the steps of: a) calculating along the hydrocarbon-bearing formation layer the pressure gradient; and b) determining the in situ PVT property from the pressure gradient using an empirical relation that had been obtained by fitting a curve through previously obtained data points comprising the measured PVT property as a function of the pressure gradient. 2. The method according to claim 1, wherein calculating the pressure gradient along the hydrocarbon-bearing formation layer according to step a) comprises the steps of: a1) lowering a tool is to the first of a set of locations in that formation layer, which tool comprises a central conduit having an inlet and being provided with a pressure sensor and a fluid receptacle having an inlet opening into the central conduit; a2) making an exclusive fluid communication between the formation and the inlet of the central conduit; a3) allowing formation fluid to enter into the fluid receptacle and measuring the pressure build-up until no change in measured pressure is observed to obtain the fluid pressure; a4) moving the tool to the next location, and measuring the fluid pressure for that location, and so on until all the fluid pressures at all locations have been measured; and a5) calculating the pressure gradient. 3. The method according to claim 2, 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. 4. The method according to claim 3, wherein making an exclusive fluid communication further includes activating a heating device arranged near the probe to heat the formation fluid. 5. The method according to claim 2, wherein the borehole is cased and wherein the step of calculating the pressure gradient along the hydrocarbon-bearing formation layer according to step a) comprises the steps of: a1) making a plurality of perforation sets through the casing wall into the formation layer; a2) lowering the tool into the cased borehole to the first 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 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; a3) setting the packers so that the perforation set is straddled between the packers, allowing formation fluid to enter into the fluid receptacle, measuring the pressure build-up, and determining the fluid pressure; a4) positioning the tool near the next perforation set, and repeating step a3) until the fluid pressures of a predetermined number of locations have been measured; and a5) calculating the pressure gradient.