The Hamaca Project is a large resource base of Extra Heavy Crude Oil (7 to 9 API), located in the Faja oil belt, to the north of the Orinoco River, in Venezuela. Petrolera Ameriven (PA), an operating agent owned by Petroleos de Venezuela S.A., ConocoPhillips and ChevronTexaco, is developing the Hamaca extra-heavy crude oil project. Field start-up occurred in September 2001, with production from a few horizontal wells. Development drilling and field appraisal is ongoing, prior to start-up of the Upgrader and commercial production at about 190 Mbopd.

Prior to start up of the field, a requirement existed for high quality samples of reservoir fluid to be obtained, for use in PVT and special core analyses, to aid in the prediction of reservoir performance. The general belief that recombination of oil and gas could not achieve a truly representative reservoir fluid sample led to the requirement to obtain reservoir fluid samples that had not experienced significant pressure depletion.

In the development of the system employed, a rigorous review was made of available downhole sampling equipment. Instead of taking pressurized samples downhole, a rod driven progressive cavity pump (PCP) was used to pressurize the reservoir fluid and deliver it to surface, where samples were collected. The fluid pressure, at all levels above the pump, was greater than reservoir pressure, insuring high quality samples. This also required surface equipment to operate at higher than normal pressures, as compared to normal PCP operations.

Every aspect of the system, and operating procedure, were examined and refined to minimize the possible pressure drop between the zone being sampled and the PCP intake. Using this system, single-phase fluid was captured at surface. This fluid, which had never experienced a significant pressure drop, was delivered to the lab, where PVT analysis confirmed that the formation fluid was at near saturated conditions, at reservoir pressure and temperature.

In addition to about 4 liters, per zone, of single-phase sample for PVT analysis, approximately 45 liters were obtained from one zone for use in special core analysis studies, which would have been too expensive to obtain by conventional methods. The costs incurred in obtaining the large volumes of sample, by the single-phase pump to surface technique, were less than prior expenditures on more conventional downhole sampling operations, where small volumes of varying quality sample were obtained.

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