Ultra-Low Invasion Fluids: A Viable Technical Solution to Drill in Eastern Venezuela

Abstract

Abstract One of key tasks of the drilling fluids industry for many years has been to develop a fluid with as low invasion characteristics as possible. These are often referred to as low invasion or ultra-low invasion fluids. If we could sop invasion by the drilling fluid completely, it would be possible to eliminate several forms of wellbore instability, lost circulation and differential pressure sticking. In addition, well productivity improvements will be expected as there will be little or no formation damage from the drilling fluid. This scenario of zero invasion is not achievable with a fluid used in an overbalanced condition, at least not in the near future. However, the industry is working to understand the benefits of he next best thing: Ultra-Low Invasion Fluids (ULIF). This paper presents the application of this technology to drill a development well in the San JoaquÍn field of Eastern Venezuela. Introduction The San JoaquÍn field, located near the city of Anaco, has been developed for several years. Thus drilling operations are subject to multiple low pressure zones that are prone to extensive losses and differential pressure sticking, resulting in down time which increases considerably the cost of the operations. Our objective with the ULIF technology was to designed and apply a drilling fluid that would enable the operator (PDVSA GAS) to drill through the 12 ¼" and 8 ½" sections with a minimum of problems. In this paper, reference is made to initial fluid properties, monitoring of fluid properties and of the concentration of the additive that produces the ULIF. Maintaining adequate ultra-low invasion properties during drilling is very important as this property provides the nearly impermeable seal that enhances borehole stability, reduces fluid losses and prevents differential pressure sticking. Following this approach, it was possible to reach total depth without any significant mud-related problems. In addition, losses were significantly reduced with respect to offset wells in the area. Analysis of performance after the well was finished showed that this application of ULIF technology resulted in a reduction of 60% of fluid losses in the 12 ¼" hole and of 30% in the 8 ½" section. Additional savings were obtained by a reduction in non-productive time and remedial procedures. Several offset wells were used to make a comparison of the performance of the ULIF in this test well. This analysis showed the cost effectiveness of the technology to drill in this area. This technology is applicable to -and it has been used in- areas where similar lithological and pressure conditions are present, namely low pressure, high porosity formations. In addition, this type of fluid can be used where high differential pressures can be a problem and where formation damage protection is of paramount importance. Description of the ULIF Technology The composition and properties of the ULIF additive has been the topic of extensive attention in other publications (Reid, P and Santos, H. 2003; Reid, P, Santos, H and Labenski, F 2004) thus it will only be reviewed briefly here.