Baroid

Design of drilling and completion fluids reduces formation damage in reservoir zone of gas wellsLocation: Yucal Placer / Lezama-Guarico,

Venezuela

OPERATOR’S CHALLENGE – YPERGAS reported a skin damage up to 25-30 during a previous drilling campaign (2004) in the Yucal-Placer wells. The reservoir section was drilled using an invert emulsion, which was recovered and reconditioned from the 12 ¼-inch section with a density of 12.5 lb/gal and a oil-water ratio (OWR) between 70/30 a 80/20. The reduced return permeability of the reservoir could have been attributed to:

• Pore size distribution tests were not performed to the reservoir rock to determine the concentration and dimension of the calcium carbonate as bridging agent.

• The use of strong emulsifiers in the invert emulsion. It is known that an invert emulsion can affect the gas reservoir’s permeability, especially when the pore throat size is small. In such case, the capillary forces in structures that small can be significant.

• Poor well cleaning job; inefficient techniques for chemical-mechanical removal of the filter cake from the wellbore walls were used.

• Reservoir section was perforated directly with completion fluid (CaCl2), with no consideration of using additives to prevent pore structure blocking.

For the N1-05 well, YPERGAS presented the challenge to Halliburton Baroid to design an integrated solution including drilling and completion fluids, as well as a wellbore cleaning strategy (post-drilling) that would minimize damage on the reservoir. The target skin effect was less than 5.

HALLIBURTON’S SOLUTION – Based on knowledge from the previous well Halliburton Baroid applied the Technical Process to design an integrated solution to meet all of the drilling and completion challenges of the well. A customized solution would help maximize reservoir potential.

 The solution included:

• Pore size distribution analysis of the reservoir section from offset wells through porosimetry, scanning electron microscope (SEM) and electron microscope to determine the optimal size of bridging materials to enable reservoir protection while drilling.

• Use Baroid’s proprietary WELLSET™ software with aloxite discs of 5, 10 and 20 micron to simulate and determine the optimum design of the bridging package. This guarantees an effective sealing of the formation according to the pore throat size.

• Use the BAROID 100 system (100% OBM) instead of an invert emulsion system, to avoid blockage due to emulsion (passive emulsifiers) within the fine porous structure of the reservoir rock.

• Keep tight control of HP/HT filtrate bellow 4 ml/30 min and PPT values less than 8 ml /30 min to minimize the invasion of the fluid to the formation, by additions of DURATONE® HT filtration control agent with ADAPTA® filtration control agent on hand as contingency.

• Use CFG™ Completion Fluid Graphics proprietary software to design chemical train of pills to achieve an efficient cleaning of the wellbore, removing any external agent that could induce skin damage.

• Use LO-GARD® service for fluid loss control to prevent water blocking, combined with a pill of CFS™-485 microemulsion casing cleaner in order to reduce the entry of water-based fluid during the perforating. CFS-485 additive would remove any emulsion that could be formed when the completion fluid comes in contact with the filtrate of the oil-based fluid in the invasion zone.

Reservoir Fluids Solutions

Case History

Baroid

ECONOMIC VALUE CREATED – YPERGAS exceeded the production target by 30% per day on N1-05 well with the application of this customized solution for the drilling, completion and WBCO (wellbore cleanout) operations in the reservoir. A similar solution was applied, with further customization to the bridging package, on the N1-06 well which also achieved 30% higher gas production per day than expected. N1-05 had an estimated skin factor of 8 and N1-06 a skin factor of 3.7, evaluated from a pressure build up analysis. These results were possible through the customized fluids plan.

©2012Halliburton.All rights reserved.SalesofHalliburtonproductsandserviceswill be inaccord solelywith the termsandconditionscontained in thecontractbetweenHalliburtonandthecustomerthatisapplicabletothesale. H0931906/12

www.halliburton.com