PDVSA operates the RG-231 and AM-102 wells, located in eastern Venezuela. The wells are characterized by stratified reservoirs and complex geology due to the presence of low permeability and porosity. The RG-231 well is in a gas reservoir with extremely low permeability (less than 0.02 md). During a well-testing operation, additional perforations were added to increase gas production. The AM-102 well was in an oil reservoir.
To effectively meet the operator's needs for a method that would help to optimize well productivity and costs without compromising the results of the operation, a change from traditional perforating operations was required. A propellant-assisted perforating method to optimize well productivity while maintaining stringent health, safety and environmental standards was proposed. The propellant-assisted perforating method uses standard perforating components and procedures; thus, it was capable of providing the necessary safety features. The propellant is essentially an oxidizer that creates carbon dioxide gas at extremely high peak pressures in the milli-second time regime to overcome in-situ stresses and create perforation breakdown and mild fracturing near the wellbore.
This paper will focus on the method developed to satisfy the operational challenges specific to the PDVSA wells. The discussion will cover the results obtained by using propellant technology in a low-permeability, low-porosity reservoir as well as how the technique was capable of addressing the operator's requirements in data acquisition as well as the difficult reservoir conditions. Instrumental in the success of the methodology was the combined use of super-deep penetration technology and propellant assisted perforation.
Santa Rosa Field. The field is located in Eastern Venezuela approximately 3 miles east of the Anaco Town of Anzoategui. (See Fig. 1 for map of the area.) The field is in one of the traditional gas producing areas in Eastern Venezuela and has 290 drilled wells. Gas projects are very important for the economics in this area, and every effort is made to increase the production from proved non-associated gas reserves.
Two distinct sandstone formations: Merecure and Colorado produce the gas. During the drilling of the RG-231 well, the San Antonio formation was discovered below the "corrimiento de Anaco" in addition to the known Merecure and Colorado sands. The San Antonio Formation, naturally fissured sandstone, is located at a measured depth of 13,000 ft.
To evaluate this new pay zone, a rigless operation was chosen over a conventional drill stem test (DST) because of the operational flexibility required in this project. Due to the anticipated extremely low flow capacity (kh) and the requirement to determine the capability to deliver gas, alternative perforating techniques to establish reservoir connectivity in lieu of conventional hydraulic fracturing were considered. To fully assess each individual sand layer's contribution to production, a series of production logging tool surveys (PLTs) for this well test evaluation were planned. The PLT surveys allow for determination of individual layer productivity and help to make proper decisions during the well evaluation. Following the PLT survey, if the sands were not producing adequate amounts of gas or fluid, they were targeted for specific stimulation treatments. To allow for complete access to the data collected during the well test evaluation, a Real-Time Operations (RTO) link was established during the well evaluation so that technical advisors could monitor and change the testing program as the data streamed across the internet to their home-based work stations. All intervention options under consideration, equipment, and procedures had to meet strict health, safety and environmental guidelines, minimize the formation damage, and properly balance the benefit/cost relationship.