The deep reservoir sandstones of the El Furrial and Pirital oilfields, located in northern Monagas state, eastern Venezuela, are famous for their high degree of geological complexity and heterogeneity. Typical well completions in this area consist of natural flow from multiple intervals through perforations in cemented casing. However, conventional perforating guns used in these completions cause additional near-wellbore formation damage that adversely affects well productivity and results in reduced productivity indexes in these wells.There have been significant efforts in recent years to implement new methods and technologies to produce cleaner perforations and better production rates. One of these technologies is a new dynamic underbalance perforation system which allows precise management of the underbalance differential pressures to produce a relatively clean perforated tunnel while minimizing formation damage. Application of this system results in improved connectivity between the reservoir and wellbore which allows substantial improvement in oil production rates.Formation petrophysical properties are used to determine whether an interval is a suitable candidate for application of this technology. A separate nodal analysis model is created for every reservoir interval in each well. These models are designed to represent the actual and expected production conditions and account for reservoir heterogeneity. In the El Furrial and Pirital fields, reservoir properties can vary widely: permeabilities from 0.1 to 1,000 mD; porosities from 9 to 18%; oil gravities from 22º to 32º API; static pressures from 6,000 to 8,000 psi; and confined compressive strengths from 7,000 to 20,000 psi. This paper presents case histories from wells in eastern Venezuela to illustrate the production benefits derived from this advanced perforating system technology. In three wells, supporting evidence demonstrates that near-wellbore damage caused by this new innovative underbalance perforation system is close to zero, resulting in over 100 % increase in the productivity index. In the fourth case history, we discuss the reasons why the actual well production rates did not achieve the rates projected by nodal analysis.
IntroductionDiscovered in 1986, the El Furrial field is currently considered to be one of the largest oil producing fields in Venezuela, with a current production rate of approximately 425,000 BOPD. Located on the north flank of the eastern Venezuela basin (Fig. 1), the field is currently produced and operated by Petroleos De Venezuela S.A. (PDVSA). Since its discovery, it has produced over 2 billion bbl of approximately 25 o API oil. Proven reserves total over 4.1 billion bbl and estimated oil in place is more than 8.6 billion bbl.
