The paper will present lessons learnt to mitigate the stabilization of the air/gas entering into lubricious biopolymer water-based system which decreased density of mud while drilling. The system selected for its highly lubricious properties and formation damage free properties to accommodate the usage of resistivity equipment provided excellent results in the field. Performance was almost equivalent to non-aqueous drilling fluid. However, the stabilization of gas/air entering the mud was encountered generating drilling troubles and risk of well control problems. An extensive study performed, consisted of assessing interactions between components and containments of the mud system with gas/air, crude-oil and drill solids introduced from the reservoir. The testing involved the adding of air from air-compressor for 60-second while mud sample is sheared at 6000 rpm. The mud weights of samples were measured before addition of air, right after and 60-second after the aeration. The percentage of density drop was calculated. Target value was maximum drop of 5% within 60 second after stopping the addition of air. Several combinations of polymers, lubricants, contaminants and other additives were evaluated. The study demonstrated that the interactions between crude-oil, polymers and lubricants can highly stabilize air/gas entrapment in the biopolymer water base mud system. The phenomena led to significant density decrease, drilling troubles, well control and safety issue in the field. They can also increase the viscosity of the biopolymer mud system. However, highly stabilized air/gas entrapment can be removed by the addition of emulsion breaker at concentration less than 1.5%vol of mud. In addition, the type and nature of the lubricant plays a major role in the stabilization of air/gas entrapment. The selection of the polymers should be combined with the choice of lubricant during the design phase to minimize the gas entrapment. Knowledge gained from the study establish a new testing protocol to assess in the laboratory the air/gas entrapment close to field shear conditions. The testing protocol showed good correlation with the field. The testing protocol can be used during the design phase or for investigations. It will improve the overall design of mud system where highly lubricious fluid is needed. Combination of polymers and lubricants did also provide low air/gas entrapment tendency.

Successful completion of an open hole gravel pack well requires a deposition of a low-permeable filter cake on the wellbore to seal and protect the permeable reservoir formation during drilling and completion operations. The deposited filter cake is removed with the aid of a breaker system before the well is put on production. The placement of a breaker post gravel packing operation brings up a concern regarding the efficiency of the breaker system due to possibly limited contact with filter cake.This study was initiated to simulate the ability of a filter cake breaker system to diffuse through gravel pack carrier fluids inside a screen base pipe and gravel pack. A new apparatus simulating the diffusion and testing protocol were created and used to perform this study. During the experiments breaker system migrated/diffused through a simulated base pipe and packed proppant filled with 10.3 ppg CaCl 2 in less than 24 hours. This proves the ability of a breaker system to contact filter cake in post spot situations. This paper describes a new method built to perform simulations with the objective to calculate the diffusion time and to document the ability of the filter cake breaker to migrate and/or diffuse through a gravel pack at ambient conditions. The paper also establishes the best practices in the design of an effective filter cake breaker system and pumping operations based on the breaker diffusion/migration mechanism.

An active filter cake technology (AFT) was chosen to improve production performance in the tight reservoir following a comprehensive laboratory study to determine formation damage impact caused by previous non-damaging fluids (NDF). The AFT was successfully field trialed on two wells with production improvement vs. acid stimulated offset wells. This paper discusses laboratory data and improved field productivity. It documents reduction of torque/drag with increased rate of penetration without using a lubricant during drilling. Comprehensive laboratory testing to identify origins of deficient production was completed by thoroughly reviewing drilling and completion practices, and completion type implemented. Compatibility of base brine with formation water; formation damage impact of drilling fluids used in reservoir and effectiveness of hydrochloric acid (HCl) solution pumped through coiled tubing to destroy the filter cake constituted the first phase of the investigation. Assessment of several fluids capable of mitigating concerns was performed in the second phase. The optimization and customization of candidate fluids to address all challenges was the third phase. Last phase consisted of field trials and assessment of production results. Testing identified a potential incompatibility of calcium chloride brine and the formation water. The brine was replaced with monovalent halides brine. The previous NDF system exhibited elevated filtrate volume and a high concentration of acid insoluble materials which together significantly impacted productivity. Review of the completion operation and laboratory results proved filter cakes of reservoir drill-in fluids (RDF) cannot be homogenously and entirely removed with HCl solution using coiled tubing. Only less than 50% of the wellbore length can be accessed with coiled tubing and treated with acid. The acid treatment dissolved less than 10% of filter cake when sumulated field conditions in the laboratory. Likewise, the filter cake breaker cannot be implemented on barefoot completion as its volume is totally lost to the formation after breakthrough before complete filter cake dissolution occurs. The study recommended AFT with 100% organophilic bridging materials. The AFT was successfully field trialled in two wells. Post analysis of drilling parameters with AFT exhibits lower torques without addition of lubricant compared to previous fluid along with 186% increase in average rate of penetration which saved 79 hours of ILT/well. Production kicked-off without assistance from lighter fluid (N2 gas) or stimulation showing promising results compared with near-by wells. The 100% organophilic bridging materials were used for first time in field. It proved acid stimulation can be eliminated for the tight reservoir while improving the oil production rate compared to the offset wells. In addition to inherent productivity improvement characteristics, AFT is appropriate where cheesing and greasing of RDF are common problems with lubricants. AFT demonstrates reduced torque without lubricant addition in extended horizontal deviated wells and excellent production while eliminating post stimulation.

Lessons learned in Moho-Nord field Congo improved well productivity and injectivity, from Miocene formation. Due to the type of drill-in fluid used in the initial development phase of the field, the skin factor showed extremely high values, above 150. The values dropped to near 50 after remediation and stimulation operations. Productivity and injectivity rates were significantly poor and did not meet the targets. To mitigate these issues, the most suitable fluids for drilling, completion and removing the filtercake for a horizontal open hole standalone completion were required. Fluids were identified by an extensive laboratory study. The selection was based on the reservoir characteristics and sand control completion type. It was also based on review of past experiences from the original project phase, and continuous discussion between operator and the fluids provider. Changes were made to improve practices during the field implementation. One reservoir drill-in fluid (RDF), a reversible invert emulsion (RIE) non-aqueous base mud (NABM) system and two filtercake breaker systems were selected and implemented in the field. The RIE showed suitable properties required for NABM drilling. It also demonstrated properties of easier filtercake destruction when exposed to lower pH breaker fluids. Its filtercake did not need surfactant/solvent pills to change the wettability of the solids in the filtercake which notably simplified the borehole cleanup operation. The improvement occurred throughout the second and third phases of the field development. The ameliorations were measured through skin value, production and injectivity rates and initial flow initiation pressure. Values were compared against initial targets. As an example, the skin value went from 150 in phase one to less than 5 in phase three. No acid stimulation was required in any of these wells, providing a huge cost saving for the operator. The combination of the fluids selected, and improved drilling and completion practices led to skin values for most between 0 and 3. The productivity and injectivity outperformed and surpassed expectations. Knowledge gained from the study re-established the importance of selecting the suitable fluids systems and using best in class drilling and completion practices. This paper summarizes upfront fluid design requirements and fluids management procedures implemented during drilling, completion and filtercake breaker placement to ensure safe and successful open hole completions.

This paper describes the development and qualification of an oil-based gravel pack carrier fluid. The fluid is a water-in-oil emulsion prepared with base oil, brine, and emulsifier. Densities up to 13.6 lbm/galUS can be achieved using oil-to-brine ratios between 45:55 and 60:40. This oil-to-brine ratio range is such that the fluid exhibits low viscosity and Newtonian rheology, making it suitable for alpha/beta gravel pack placement. Extensive laboratory testing was performed to characterize fluid properties at various temperatures and oil-to-brine ratios. Performed in 4-in pipe, tests evaluated pressure drops at rates of up to 15 bbl/min, which revealed that the friction pressure generated by this fluid matches established empirical correlations for Newtonian fluids in turbulent flow. Finally, a full-scale yard test was performed to demonstrate that the fluid can be mixed using standard mixing equipment and used to successfully place alpha/beta gravel packs.