Channeling behind casing connecting two sandstone reservoirs in well 13 was suspected due to poor cement job, possibly due to the high angle well of 76 deg. Avoiding communication behind casing between two sands is detrimental for field reservoir management where reservoir pressure maintenance with water injector wells is paramount for continuous production. This paper describes the treatment background, engineering approach, laboratory testing and QA/QC procedures, fluid design stage and job execution using the propriety low viscosity polymer system to seal off channeling behind casing. Cement bond log performed in well 13, a 76 deg. directional well drilled offshore Peninsular Malaysia showed very poor bond behind casing. An injectivity test conducted by setting a retrievable packer in between perforation intervals of the two sand bodies near the suspected channeling confirmed communication between the two sands. Repair alternatives were evaluated opting between cement or polymer gel squeeze. Hydraulic calculation based on the injectivity test result, roughly set the equivalent channel diameter as 0.15 in. Cement squeeze was therefore rejected in view of the small and long cement channel of 109 m. An alternative method to squeeze a low viscosity polymer system into the channel behind casing was hence designed for the purpose of sealing off the channel. The procedure developed was to create a single perforation in between the two perforations in both reservoirs and squeezing the polymer. A retrievable bridge plug and a retrievable packer straddled the squeeze perforation interval and a polymer gel squeezed through the said perforation. After several squeezes each followed by a curing time, pressure tight seal isolating the two reservoir sands was obtained. This was confirmed by setting a retrievable packer above the lower most perforation in the reservoir sand followed by injecting brine while monitoring for returns through the upper perforation, which were none. This unique method, never applied before, to repair a 109 m continuous cement channel between two reservoir sands separated by a thick shale layer using cross linked gel was successful. Two years later the seal is still intact with production from this dual completion well continuing trouble free. The proprietary gel applied is a cross linked low viscosity polymer which cures under downhole temperature to form a tough seal. It is learned that running a retrievable bridge plug and a retrievable packer in tandem in high angle well best not be attempted in future, instead, both should be run separately. Acidizing through the squeeze perforation will assist to improve squeeze pressure. Application of cross linked gel to repair cement channel has been proven to be a viable alternative to cement squeeze.

Most of the S oil field producers experienced rapid decline in production and this is suspected due to fine sediment particle migration and plugging. The S field team had carried out external formation damage study as they have no expertise and field experience to determine the damage mechanism and evaluate the best acid treatment recipe for their formation damage. Recently, mixtures of traditional hydrochloric and hydrofluoric acids have been used for the removal of near-wellbore damage in S field sandstone formations. The stimulation campaign in this field which has turbidite reservoir, high clay content predominantly by kaolinite and illite with high siderite mineralogy applied both bullheading and coiled tubing squeezing techniques. The treating fluid selection is highly dependent on mineralogical data and laboratory works. Based on the core flood testing performed, high strength mud acid is chosen as the main treatment fluid and gave superior result in permeability recovery as compared to milder organic acid and HF. Unfortunately, the actual field stimulation turned out to be opposite from the core flood testing outcomes. The situation is worsened in multistage treatments, which traditionally involve many repeat stages of preflush, main treatment, overflush and diverter. The mud acid stimulation prompted more water production and fine migration that is ended up with production curtailment. Only one out of four of the treated candidates resulted significant gain after gas lift valve change took place. This paper also will outline the reviews on results of laboratory testing and field actual performance together with the recommendations for future improvement. Stringent candidate selection, improved treatment fluids cocktail, operational challenges such as unanticipated longer flow back period, post treatment unwanted precipitation, ineffective diverter placement and skin build up post treatment are among of the learning points captured in this paper. From this unfavorable mud acid stimulation campaign which cost USD4million value leakage, our team comes out with best practices for future stimulation and key learning to share with industry colleagues who has no field background to combat with fine migration issue in their sandstone asset. Laboratory works is not the only paramount to any stimulation, success in stimulation is a journey, not a destination. The doing is often more important than the outcome.

Restoring formation damage by acid matrix treatment in sandstone formations faces multiple challenges due to variable petrophysical and compositional properties. The S field team had carried out a formation damage study to determine the damage mechanism, evaluate the best acid treatment recipe to treat the formation damage mechanism identified and study the effect on petrophysical properties before and after the treatment. Most of the S field oil producers experienced rapid decline in production, and this is suspected to be due to fines migration and plugging. The formation damage study is divided into three sections: the field background review, the potential formation damage identification, and the evaluation of the best acid treatment recipe for S field formations. Core samples from a wide range of mineralogy, permeability, pore distributions and porosity were evaluated using laboratory testing to describe the elemental and morphological presence of each mineral. Then, four of the core samples were high graded for evaluating the permeability by flooding with brine and oil to examine the fines migration and dispersion potential of clays and siderite. The next phase of this study was continued with the core sample acidization using organic acid and HCl to identify a suitable acid treatment cocktail. This will be discussed in detail in this paper. Fines migration was observed to be resulted from movement of both siderite and aluminosilicate clays under representative conditions. The evidence from the geological analyses and core flooding shows that in brine, there is a tendency for siderite to migrate, potentially even at low flow rates. The effect is expected to be more severe in brine than in oil and possibly in both phases. HCl acid and strong organic acid treatments with and without the presence of an iron control to remove iron carbonates in siderites and iron-silicate gel formation will be outlined in this paper. The result of the HCl treatment was that it was able to remove carbonate material from the core, but it was still not able to substantially improve wellbore permeability. An additional short phase of testing examining a HF-HCl package was demonstrated more effective and is discussed extensively in this paper. This laboratory work is not unusual to the sandstone stimulation however the discussion of the core flood testing findings and acid recipe comparative study provides more comprehensive understanding on the effect of fines migration to the success of the stimulation treatment and its effect on petrophysical properties. The outcome of this work will lead to a reliable design of sandstone matrix acid treatments and, increase the acid stimulation treatment success rate which subsequently optimizes well productivity.