Enhanced Acid Fracturing with Improved Fluid Loss Control and Near Wellbore Diversion Increases Production in Kuwait

Abstract

Excess fluid leak-off, a challenge in Kuwait's naturally fractured tight carbonate formations, can compromise post-fracture productivity. Past acid fracture treatments, both for moderate and high temperature formations failed to generate the long differently etched fracture due to excessive leak-off. Treating zones with multiple perforated intervals in a single stage, particularly in pay zones with long heterogeneous rock properties can result in non optimal stimulation. Therefore, a new approach was developed with proven success to enhance fracture conductivity and overall production by efficient control of fluid leak-off. This novel approach incorporates the use of far-field and near-wellbore diverting systems into the acid fracture design. These solid particulate diverters (SPD) include low and high temperature systems that provide enhanced near-wellbore diversion in both case and open-hole applications. The SPD are designed to bridge across perforations and fractures in the higher permeability zones, diverting the stimulation fluid into lower permeability zones. A smaller sized multi-modal distribution of SPD controls the fluid in narrower natural fractures and wormholes, deepening penetration of the stimulation fluid along the entire fracture length. The SPD agents are fully degradable and do not contribute to permeability loss of the created fracture or the perforated interval when production starts. The production of the wells where the SPD agents were applied were higher in comparison to expected production of offset wells where non-acid crosslinked fracturing pad stages alternated with gelled or emulsified acid, and visco-elastic surfactant (VES) slugs. Both crosslinked fracturing pads, VES and emulsified acid slugs do not effectly control live acid leak off. Two case histories, documenting successes where this new approach to acid fracturing has been applied in the Tuba and Middle Marrat formations, have superior production results that correspond to enhanced fracture geometry.

Development of Acid Fracturing Model for Naturally Fractured Reservoirs

“…Williams et al (2016) conducted an experimental study on improving the acid leakoff control by using far-field solid particulate diverters which effectively bridge wormholes and hairline fractures away from the wellbore region. The field application of this type of diverters along with the near-wellbore diverters showed an improved fracture conductivity and the overall efficiency of the acid fracturing treatment in heterogeneous carbonate reservoir containing natural fractures (McCartney et al 2017).…”

“…There are multiple publications on improving the acid fracturing efficiency in naturally fractured reservoirs, many of which focus on using viscoelastic acid systems with diverters to reduce the acid loss form the main fractures by bridging the natural fractures (Rahim et al 2017;Williams et al 2016;McCartney et al 2017). However, the effect of natural fractures on the efficiency of the acid fracturing treatment and created fracture conductivity is not fully understood.…”

“…Several publications (Arangath et al 2008;Jauregui et al 2011;McCartney et al 2017) mentioned that the efficiency of acid fracturing in naturally fractured formation can be improved by using fluid loss control additives. Arangath et al (2008) reported that using viscoelastic surfactant (VES) based acid system along may not be effective enough to stimulate carbonate intervals dominated by natural fractures.…”

“…Application of a similar acid system for acid fracturing stimulation in naturally fractured carbonate reservoirs in Middle East indicated a significant production improvement compared to using acid system without fiber-laden diverters (Dashti et al 2009). Another study on the leakoff control in naturally fractured carbonates in Middle East (McCartney et al 2017) indicated that the production of the wells where solid particulate diverters, including near-wellbore and far-field diverters, were used was higher than the production of offset wells, where alternating stages of pad fluid and gelled or emulsified acid with VES slugs were pumped. All the field cases mentioned above have focused on a positive effect of leakoff control on stimulation efficiency achieved by bridging natural fractures with solid particulates or fibers.…”

Geochemical element mobilisation by interaction of Bowland shale with acidic fluids

“…Acid fracturing treatment is an effective method to stimulate the production of carbonate reservoirs. However, wormhole propagation induced acid leak-off should be controlled since it is the key to successful acid fracturing [14,15]. Water that returns to the surface after hydraulic fracturing and before production is referred to as flowback water, and the produced water returns from the formation [5].…”