Abstract

The marine light crude (CLM) project in offshore Mexico is a group of 12 oil fields located 75 km off the coast of southern Mexico (Jurassic and Cretaceous period). The fields have been under development since 2003, are high-temperature (160°C or >300°F) carbonate formations producing gas and condensate with permeability that ranges from 1 to 6 mD, and are naturally fractured. These fields were experiencing considerable drawdown, which slowed down the return on investment and, in one case, could have potentially led to well abandonment. Established dogma dictates that carbonate formations in Mexico are best treated by matrix stimulation rather than fracture-stimulation techniques. The two case studies discussed in this paper demonstrate the effective implementation of a production-optimization design and execution methodology that has translated into productivity increase. The design resulted in up to 80% removal of the pressure drop experienced in the formation face, accomplished by establishing a linear flow path, bypassing the formation damage. After treatment, a production increase of 50% more than conventional treatments is the best proof of concept, validating the synergistic approach, entailing data collection and analysis, field and laboratory work, and engineering design and simulation. The selection of appropriate candidates was performed by analyzing productivity data (drillstem testing), which indicated a skin factor of zero but, nevertheless, a remnant and considerable pressure drop caused by the formation's low permeability. Fluid optimization and placement techniques were combined with core studies and rock mechanics in the job design. Candidate wells for acid fracturing had permeability of 1 to 20 mD, while matrix stimulation candidates had 20 to 50 mD, and 50-m etched fractures appear to have provided optimum results. The methodology signifies less risk of incurring damage caused by condensate formation in the formation. As a result, fracture acidizing in Mexico's offshore fields is a completely viable alternative to production improvement.

Introduction

The use of various fracturing methods for stimulation of wells has become a common procedure in the oil and gas industry. Fracture treatments are performed on wells with varying potential to help increase production and reduce the drop pressure on the face formation. Many hydrocarbon-bearing carbonate formations are routinely stimulated by fracture acidizing, and the use of fracture acidizing to enhance the production of carbonate formations continues to be an effective process. Numerous authors have investigated the factors that affect the production increase of a fractured well, including special acid systems and placement techniques, etc. However, to achieve a successful fracture-acidizing treatment, three fundamental issues must be addressed:

  1. reactivity control,

  2. fluid-loss control, and

  3. conductivity generation (Gdansky 2005).

The desire for increased production is concurrent with the need to optimize treatment designs and predict what increases might be expected.

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