Stimulation of wells completed in multiple layers has always remained a challenge with regards to stimulating all the layers uniformly and effectively. Problems are more severe if the sub-layers of the formation have different petro-physical characteristics and have varying degree of permeability contrast. Stimulation treatments without diversion system applied in these multi-layered wells mainly stimulate the high permeable streaks repeatedly. PH and temperature sensitive In-Situ Cross-linking Acid Diverting Agent (ISCADA) is developed to temporarily block the high permeable or undesired layers. This diverter chemical with maintained pH is cross-linked in-situ at reservoir temperature. Breaking time of the diverter could be tailor-made by optimizing the breaker depending upon the requirement of treating time. The diverting agent has the advantages of breaking on its own and clearing the blockage of the high permeable zone to regain its initial permeability while facilitates the acid to stimulate the desired zones. The alternating stages of diverting agent, retarded acid and main acid can be designed as per the well conditions. ISCADA can be applied in both sandstone and limestone reservoirs. Trial application of ISCADA system was done in the limestone formations of Mumbai high field and other sandstone reservoirs. Substantial improvement in productivity observed using ISCADA as diverting agent and subsequent application of compatible acid formulation. Remarkably water production has come down in some wells. This paper outlines the laboratory development of the diversion stimulation system; case histories of its application in limestone and sand stone reservoirs. Introduction Stimulation of multi-layered wells has always a remained challenge with regards to uniform and effective stimulation of all the layers. Stimulation treatments without diversion system applied in these heterogeneous multi-layered wells mainly stimulate the high permeable streaks repeatedly leaving other layers untreated. With the aim of stimulating the multi-layered wells uniformly, efficiently and cost-effectively an acid diversion system is essential. In the context of Indian reservoirs diverting acid into untreated zones has remained great challenge in the thick, and high permeability onshore sandstone formation as well as multi-layered carbonate formations in the offshore. Diversion is the process by which the treating fluid is diverted from high permeable zone and allowed to enter the lower permeable zone, thereby making the homogenous distribution of treating fluid in the zones of interest. A critical factor to the success of an acidization treatment is proper placement so that designed volumes of treating fluids contact productive intervals. Effective placement of the treating /stimulation fluids evenly across the zones of interest is important specially when treating long perforated intervals or multiple zones. If there are significant variations in reservoir permeability, the acid will tend to flow primarily into the highest- permeability zones, leaving lower- permeability zones virtually untreated. Even in relatively homogeneous formations, the damage may not be distributed uniformly without the use of techniques to improve the acid placement; much of the damage may be left untreated. Thus the distribution of the acid into the formation is an important consideration in matrix acidizing, and treatment design should include plans for uniform acid placement. The in-situ cross-linking acid diverting agent (ISCADA) is both pH and temperature sensitive. This diverter chemical with maintained pH is cross-linked at reservoir temperature. The cross-linked, high viscous diverting agent then blocks the subsequent treating fluid to enter into the high permeable layer and divert them to the zone of interest. The alternating stages of diverting agent, retarded acid and main acid can be designed as per the well condition. This paper discusses the laboratory development of the ISCADA and general guidelines for implementation.

Due to nearby water contact, conventionally cased hole gravel pack (CHGP) was preferred completion techniques for sand prone reservoirs in western onshore basin and KG basin of India. However, these completions had often performed poorly both in terms of productivity and longevity. This paper describes the detailed case studies for new completion approach (i.e. Slick Water Frac Packing) adopted to alleviate the productivity decline including favourable modification in completion procedure & job treatment. Since inception, Cased-hole Frac Packing (CHFP) was avoided owing to incompetent shale barriers and nearby water contact. Later on, Horizontal Open-hole gravel packing and Standalone screen completion techniques were adopted but result was not encouraging. The productivity decline was further aggravated with "water-shut off" treatment prior to cased-hole gravel packing. The existing completion strategy was reviewed to identify the shortcomings & a new completion strategy of Slick Water Frac packing(SWFP) adopted for these fields, which was further customized to suit the specific well conditions. When these customized SWFP were implemented, significant improvement in well performance was seen, in form of hydrocarbon production. Till date more than thirty wells have been completed with SWFP. Among them, many wells were already producing water beyond the acceptable limit while some wells have very near water contact (< 2.5 m) without competent barriers. Apart from this, one well had long history of fines production and CHGP / standalone screen (SAS) completion applied did not give good result. The execution of customized SWFP was successful in almost all wells and amount of proppant placed in the formation was the range of 300-1000 lbm /feet of perforation. These completions have achieved the objective of productivity enhancement with average incremental oil gain of about 22 barrel per well apart from formation sand retention. Although some SPE papers have described the CHFP application in wells having near water contact, but the combination of WSO treatment and Frac packing treatment for wells already producing high water cut, is unprecedented as per author's knowledge. The information provided in this paper can be used to enhance hydrocarbon production without increasing significant water production in similar fields.

Hydraulic fracturing is the proven stimulation technique to exploit hydrocarbon reserves trapped in tight gas Indian reservoirs especially in Mandapeta field of Southern India. Fracturing technique was customized to obtain designed fracture geometry which in turn resulted in very good post frac gas production rates. This paper deals in detail, the necessity of fracturing in Mandapeta field, meager production gains obtained in earlier fracturing treatments, challenges for fracturing, quality assurance and quality control of fracturing fluid, design and successful execution of fracturing technique. Mandapeta field is located in Krishna Godavari Basin situated in Southern part of India. Customization of fracturing technique produced impressive gas production rates from Mandapeta field compared to earlier treatments. Poor geophysical properties of the reservoir, leak-off characteristics, completion constraints and high near wellbore frictions were some of the challenges observed during fracturing treatments. As the reservoir is having very low permeability, hybrid fracturing treatment with a pad comprising around 75 percent linear / slick gel followed by cross-linked slurry was designed and implemented successfully. Gas production gains up to 37000m3/d in a single well was observed. 20/40 mesh high strength proppant was used in these treatments and maximum job size pumped was 151MT. Hybrid frac treatment was carried out in an exploratory location which resulted in impressive gas gain paving a way to further development of field. Pre-frac acid treatments improved the well bore connectivity to the reservoir thereby enabling the higher proppant concentrations to pump during the treatments. Chemical compositions addressed the surface tension and mobility concerns of the fracturing in gas reservoirs which resulted in faster cleanup and gas production. Recent successes of fracturing made a way forward to aggressive fracturing campaigns in this field. Hydraulic fracturing treatments have to be customized to specific reservoir conditions so as to obtain success. Candidate selection, modeling designs using sensitivity analysis, suitable pre-frac treatments, lab studies for optimization of fracturing fluid, customized hybrid fracture treatments played vital role in successful execution of fracturing treatments in Mandapeta field of Southern India which can be applied to other tight gas reservoirs.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractFracturing in water injectors often becomes a pre-requisite to achieve the desired sweep efficiency. The requirement is more pronounced in the injectors with very poor injectivity or poor dissipation. Conventional stimulation techniques like acidisation have not proved to be beneficial. Under such circumstances, a recent foray has been made into the application of water frac.  Water frac is an efficient technique to achieve a limited-length fracture, ensuring a higher sweep efficiency in water injectors. The candidate well is selected after a detailed study by multidisciplinary team and a customized job schedule is prepared for an initial low-proppant concentration, followed by high concentration at the end to attain higher conductivity near wellbore. Due to zero polymer loading, this technique has the added advantage of low formation damage. There is also saving in chemical and proppant costs. This technique is suitable for not only water injectors, but also effluent disposal wells and polymer flood injectors.This paper describes the technique and requirements for water frac, along with the case histories. The job design and the results are discussed in details. The benefits accrued have underlined the success of this technique.

This paper discusses the Hydraulic Fracturing (HF) treatment of the Andimadam Sandstone formation of Periyakudi field of India. The Andimadam sandstone is a hydrocarbon bearing formation, with estimated in-place reserves of 47.43 MMt (O+OEG) which was prognosticated after drilling and established hydrocarbon potential. Well PD#A was drilled in Andimadam Sandstone and HF in this well was attempted in order to develop and exploit the full potential of the oil and gas reserves of the field. The fracturing treatment of the tight gas reservoir in one of the deep well in Periyakudi field was performed eld. It was a challenge to carry out HF in well PD#A at such deeper depth formation. There was no previous information available to understand the formation and to predict its behaviour during HF treatment. HF treatment in tight gas Sandstone laid so many challenges. Formation breakdown, succeeding minimum rate required for fracturing and attaining high proppant concentration during job with crosslinking gel under extremely strenuous operational conditions and pressure limitations were some of the major challenges. Delayed cross-linked gel was used to minimize tubing friction pressure. Managing the pumping rate with pressure limitations during HF treatment was one of the major challenges. Execution of the treatment with low pumping rate results in stimulation of small volume of rock comparatively. All these limitations were overcomed by proper job designing, optimization of fracturing fluid and analysis of pre-frac treatments. A substantial amount of fracturing fluid and proppant placed into the formation maintaining all safety standards. Satisfactory flow back of frac fluid with gas was observed and high flow back pressure at surface was noted. This paper discusses challenges to execute hydraulic fracturing treatment in well PD#A and the lessons learned during the execution. In addition, it was the deep well (drilled upto 4945 m) in Periyakudi field with low permeability reservoir. Post analysis of pre-frac treatments done to obtain the reservoir properties and to design the main frac treatment. The results of fracturing treatment are also discussed. The promising hydrocarbon potential of the Andimadam sandstone which are based on post fracturing analysis, encourages further future development of the Periyakudi field, Cauvery Basin, India.