First Regional Selective Packerless Acid Fracture Stimulation With Coiled Tubing: A Documented Case History From Saudi Arabia

摘要

A review of stimulation methods previously used in the Hanifa formation (primarily diesel emulsified acid/visco- elastic diverting systems) performed during the first two quarters of 2005, revealed that while initial post-stimulation vertical or deviated well performance was typically improved, it was also short-lived. All the wells exhibited a gradual loss in productivity after the stimulation treatments. Furthermore, in horizontal wells, the problem was aggravated as there is not enough control of acid placement over long open hole carbonate intervals where permeability or damage contrast exists; requiring a deeper matrix stimulation. Exploring improved methods for stimulation, a multidisciplinary team composed of Saudi Aramco and service company representatives were brought together to review various stimulation methods. After looking at conventional hydraulic fracturing as a method of deeper formation stimulation than matrix acidizing, it was concluded that over the long open wellbore intervals, there would not be sufficient control of fracture placement, fracture growth and propagation, and interaction with the natural fracturing present in the Hanifa. Additionally, the typical Hanifa completion strings have completion size restrictions which limit the options for rigless stimulations. After the review of several options, including coiled tubing (CT) proppant fracs, and stimulation using multiple discrete mechanically isolation devices like plug or packers, the team selected the Packer-Less Selective Acid Fracture (PLSAF) stimulation using CT as the stimulation method most desirable for the limitations intrinsic to the Hanifa formation for the following reasons: 1. PLSAF with CT offers control of fracture placement in an open hole environment, 2. PLSAF can achieve multiple treatments without mechanical isolation, 3. PLSAF can provide moderately deep, controlled fractures with reduced risk to connect the generated fracture with the water sources. PLSAF was applied successfully in one well during the third quarter of 2005 where 10 selective acid fractures were placed along the open hole section. This paper presents the long-term evaluation and benefits of the first regional application of the PLSAF in Saudi Arabia.