Latin America hasn't escaped the general industry trend of finding reserves in ever challenging environments. Complex geology and low permeability are the common denominator in today's environment. Developing reserves under these conditions with conventional vertical wells is in most cases uneconomical. In this setting, horizontal wells have come to mitigate the problem, however in most unfavorable conditions where oil and gas are found in tight formations fracture stimulation needs to be added to the equation. Conventional multistage fracturing techniques including perforating, fracture stimulating and isolating stages with a composite bridge plug have been applied in some cases with limited success. The time consumed in the completion operations extends over weeks making wells uneconomical. In addition, the prolonged time over which the frac fluid remains in the formation before being flowed back often affects well productivity. This paper describes the experience of three operators in Latin America that have implemented a new completion system to overcome the time consuming and productivity limitations of conventional completions described above. The new completion system is run as part of the production liner, does not require cementing and provides positive mechanical diversion at specified intervals, so fracturing and stimulations can be pumped effectively to their targeted zone. The system has also been designed, so all of the fracturing or stimulation treatments along the horizontal wellbore can be pumped in one continuous operation, thus minimizing the associated risks and optimizing the efficiencies of both the personnel and equipment needed to perform the work. The conclusions will show the operational efficiencies and reliability of this novel completion system, as well as analyze the cost benefits and production increases that have been observed. Introduction Operating companies are continuously pushing to improve hydrocarbon recovery, a task that is becoming more and more difficult as they are pushed to develop fields in more complex settings and with poorer reservoirs properties. Horizontal wells have been a tool widely used to improve both production rates and recovered reserves per wellbore in order to improve the economics of particular projects or make them commercially viable in extreme cases. Over the last two decades many developments have enabled accelerated growth in horizontal well applications. Drilling has led the way, with current technology capable of drilling thousands of feet laterally through a hydrocarbon reservoir. Drilling technology has evolved to a point where horizontal wells can be constructed at comparable costs to vertical wells while offering the advantage of higher production rates and better access to reserves. Often times fewer horizontals are required to develop a field given its larger drainage area. However horizontal well completion has lagged behind, in particular when a stimulation treatment is part of the completion or has to be applied as a remedial treatment in wells performing below expectations1.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractFor the last eight years acid fracturing stimulation has been performed in the Veracruz basin to increase gas production in naturally fractured carbonate formations. Several techniques have been proved to enhance the results of these jobs, including the diverting technique and the application of nondamaging viscoelastic fluids technology specifically a selfdiverting viscoelastic based acid system and a polymer-free viscoelastic surfactant gel for fracture initiation and propagation. This paper presents the results of successful acid fracturing treatments recently performed using nondamaging viscoelastic surfactant-based fluids to increase gas production from naturally fractured carbonate formations.Most of the wells drilled and completed in the carbonate formations of cretaceous age in Veracruz basin do not flow naturally because of low matrix permeability and drilling/completion fluids damage. Therefore, acid fracturing treatments are necessary to produce these wells at economical rates.The objective of these treatments is to increase gas production by creating a deeply etched fracture that will bypass the damaged zone and connect to the network of natural fractures and/or fissures. The etched fracture length affects well performance in low-permeability reservoirs; increased fracture length should result in greater production response. The use of nondamaging viscoelastic fluids is necessary to obtain longer effective etched fractures. Combining this with the properties of a viscoelastic diverting acid will significantly increase fracture conductivity as well as the effective stimulation of all perforated intervals.The fluids were combined by using a pumping technique that consists of alternating stages of nonreactive fluids, reactive fluids and diverter fluid to reduce wormhole creation at the nearwellbore area and increase etched fracture length.Four field cases are presented in this paper. In three, multiple intervals were treated, resulting in longer etched fractures as deduced from after-treatment production response and radioactive tracer logs. In the fourth case, not all the intervals were effectively stimulated because diversion was not used.

This paper presents the results of successful applications of Acid Fracturing to increase gas production in mature carbonate fields in Mexico. Production comparisons show a substantial improvement in well performance following acid fracturing treatments. Six case studies are provided where a systematic methodology was employed to correctly determine candidates, and treatments. The methodology discusses the use of a novel technique that consist in alternating stages of acid and a non reactive fluid. The fracture acidizing treatment technique, is designed to stop wormhole growth once growth has begun. The technique consists of initiating a fracture with a nonreactive pad of gel led fluid followed by alternating stages of alcoholic acid and nonreactive pad. This system has been chosen to overcome two main problems, those are fracture extension and well cleanup. This technique improves live acid penetration in a naturally fractured reservoir, thus sustaining greater and longer production increases than prior stimulation treatments. The benefit obtained from the used of alcoholic acid as a reactive fluid in gas wells is observed during the initial production stages, when the well cleanup is rapidly achieved and gas production established. Results of the treatments performed are discussed in details, including acid and gel volume, designs and analysis of the pressures recorded during placement, also data on load recovery times following the job are shown as wells as Prior and post fracture well analysis interpretations showing effective skin reduction and fracture length. Finally gas and condense production are presented including stability with time. P. 285

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This paper was prepared for presentation at the 1999 SPE Mid-Continent Operations Symposium held in Oklahoma City, Oklahoma, 28-31 March 1999.