Ilmenite Inclusion: A Solution towards Solid Sagging for Hematite-Based Invert Emulsion Mud

The sagging tendency of hematite in drilling mud is a common challenge occurring at high-pressure and high-temperature (HP/HT) applications. This work studies the performance of hematite-based invert emulsion mud for HP/HT conditions and provides a solution to prevent the hematite settlement using a combination of ilmenite with hematite. Practical mud formulation was utilized over a range of ilmenite/hematite ratios (0/100, 20/80, 40/60, and 50/50%) to study sagging behaviour. From the sag tests, the optimum combination proportion was determined. Thereafter, the density, emulsion stability, rheological and viscoelastic properties, and filtration conduct for the formulated mud were evaluated. The experiments were conditioned as per the standards of the American Petroleum Institute. The obtained results of sagging experiments indicated that including 50% of ilmenite mitigated the hematite settling and reduced the sag tendency towards the safe range. A slight drop (4%) in mud weight was noticed upon adding the ilmenite, whereas the emulsion stability was enhanced from 551 to 574 volts with the 50% ilmenite content. The rheology and viscoelasticity measurements showed that 50/50% combination improved the yield point (YP) by 50% with a trivial 1 cP increment on plastic viscosity (PV), hence enhancing the YP/PV ratio by 46%. Also, the gelling strength was enhanced resulting in flat rheology and better gel structure. The filtration behaviour of 50% ilmenite mud was improved compared to blank hematite as it resulted in 21, 15, and 17% reduction on the filtrated volume, filter cake weight, and thickness, respectively. This study provides a solution for hematite sagging issue at HP/HT using combined weighting agents, which contributes to enhancing the mud stability and avoiding several well control issues and related operational and technical challenges that eventually will economize the drilling cost and time.

A Customized High Performance Water-Based Mud Solved the Challenge to Drill Reactive Shale Formation and Simplify the Logistic Challenge in an Exploration Well in Offshore East Kalimantan, Indonesia

Exploration drilling obviously requires a robust drilling fluid system to be a key factor in overcoming both the known and unexpected challenges of a structure that consists of reactive clay and lost circulation zones. Extra consideration has to be given to regulatory environmental requirements and complications resulting from regional politics. A High-Performance Water Based Mud (HPWBM) system was selected to address the aforementioned issues. The HPWBM was customized to respond to the subsurface conditions with the main requirement to provide maximum shale inhibition through a non-dispersed environment. Polyamine was utilized to stabilize all types of clay; an encapsulation polymer and a non-ionic polymer were included to prevent dispersion and to seal micro-fractures. A complete shale study was performed to determine the optimum concentration of the base fluid and each shale inhibitor. Then hydraulic behaviour of the mud was simulated with contractor proprietary software to understand the parameters for optimal hole cleaning as well as Equivalent Circulating Density (ECD) simulation. The HPWBM system successfully facilitated the execution of the exploration well and provided highly effective clay stabilization. No Non-Productive Time (NPT) was recorded as a result of reactive clay issues. The mud system also facilitated a good rate of penetration (ROP), formation stability, and lubricity. Waste cuttings transportation was not required. In addition, there is also no requirement for costly base oil including its associated transportation costs. The successful implementation of the HPWBM yielded an estimating saving of 25% compared to invert emulsion fluids, prior to considering costs associated with an expensive Liquid Mud Plant (LMP), environmental, and freight costs. Significant cost savings were achieved by eliminating the need for LMP rental, mobilization and demobilization. Another notable saving was realized from the reduced system maintenance of the HPWBM as less dilution was required compared to a regular Water Based Mud. Thinking outside of the box and embracing the departure from the default consideration of an invert system with a thorough risk assessment augmented value to wellbore construction. A smartly designed HPWBM system provided performance comparable to an invert emulsion system but with superior benefits with respect to environmental protection, simplified logistics and lower costs.

Innovative Surfactant Chemistry Offers the Performance Advantages to Invert Emulsion Drilling Fluids While Drilling Under Challenging Environments

Stable invert emulsion with oil wet solids is achieved using invert emulsifiers and wetting agents. This paper reviews the chemistry and performance criteria of traditional invert emulsifiers and wetting agents utilized in formulating stable invert emulsion drilling fluids. However, occasionally such stable invert emulsion drilling fluids can be destabilized due to various hostile conditions encountered during drilling operation, and can adversely impact the drilling cost. Extreme preventive measures cannot avoid such hostile conditions such as sudden water influx, excessive solids and salt contaminations during drilling. Upon solids becoming extremely water wet with "flipped emulsion", it becomes impossible to fix the drilling fluid, resulting in expensive maneuver. Often situation cannot be corrected with traditional wetting agents and emulsifiers even at high level of treatments. New innovative chemistry addresses the severe water-wetting and emulsion instability of invert emulsion under extreme challenging and hostile situations. The unique water soluble oil mud conditioner (OMC) synergistically enhances the performances of traditional oil-wetting agents and emulsifiers at very low, as little as 0.5 ppb levels of treatment. This OMC improves and extends the efficacy of the traditional invert emulsifiers and oil wetting agents resulting in reduced usage of these additives with excellent economic advantages. The 15.0 ppg, invert emulsion drilling fluids were prepared using 2-3 ppb of primary and secondary emulsifiers, and these fluids were destabilized using high shear mixer for 7-8 hours. The destabilized fluids had severe water wet solids and ES value of less than 5. These destabilized fluids, upon treating with 0.5 ppb of newly developed OMC instantly became oil-wet and shiny and ES was increased to greater than 500. To demonstrate the effectiveness of OMC in pre-treatment situation, the base fluids treated with 0.5 −1.0 ppb of OMC showed superior mud stability compared to base fluid when contaminated with sea water, fine solids, barite and high salt contaminations. The OMC is flexible in its application and can be used as pre-treatment to improve the overall performance of drilling fluids and can also be used for post-treatment to recover the drilling fluids, which have been rendered unusable.

Fate of Emulsifier in Invert Emulsion Drilling Fluids: Hydrolysis and Adsorption on Solids

Emulsifier concentration in SBM is an important factor of drilling fluid stability. Proper concentration of amidoamine emulsifier is imperative for controlling low fluid loss and maintaining emulsion stability. This study investigates the physical and chemical interactions between emulsifier and other additives and describes the processes by which emulsifier is depleted from the drilling fluid. Three main pathways of emulsifier consumption are identified: emulsifier adsorption on solids found in drilling fluids and low gravity solids (LGS), chemical degradation, and to stabilize the invert emulsion. Design of experiments model and analytical procedure based on 1H NMR (nuclear magnetic resonance) spectroscopy was used to quantify the required emulsifier concentration in Non-Aqueous Fluid system (NAF). Additionally, model systems were used to estimate the excess of emulsifier, evaluate the emulsifier losses due to alkaline hydrolysis at elevated temperature, and measure adsorption of emulsifier on barite and various LGS types. Calculations for emulsifier depletion based on model systems were correlated to performance of formulated drilling fluids for verification. Typical emulsifier requirement in high performance NAF is 8-12 pounds per barrel (ppb). Majority of the emulsifier is adsorbed on weighting agents (barite) and rheology modifiers (clays), which are used to formulate NAF, that contribute to their effective dispersion in the solution and control fluid rheology. The adsorption process is found to be sensitive to the emulsifier concentration, solids mineralogy, wetting agent and temperature. Analytical Langmuir-Freundlich isotherm was used to describe adsorption data and estimate the adsorption capacity of the system. The emulsifier degradation pathway is another important factor of emulsifier consumption; however, emulsifier degradation at 250°F is not significant. While NAF are generally run ‘rich’ to mitigate depletion and maintain fluid stability, adsorption onto minerals will become an issue especially at high LGS concentration. These results will be greatly beneficial in the further development of NAF drilling fluid formulations and will assist field engineers in understanding the effect excess emulsifier will have on the drilling fluid and enable them to more effectively control the fluid properties under variations in emulsifier and LGS concentration during drilling.

Next Generation High Performance Invert Emulsion Drilling Fluids with Flat-Rheological Behavior

The rheological properties of drilling fluids are crucial parameters for efficient drilling operations. Invert emulsion drilling fluids are the industry's preferred choice when it comes to extreme conditions like deepwater or high temperature and high pressure (HTHP) drilling due to their inherent thermal stability and effectiveness against water sensitive formations. In addition, another highly desired property of such drilling fluids is minimal sensitivity of the fluid flow properties for a wide range of application temperatures, known as flat-rheology behavior. We have developed four novel and next generation chemical additives: (i) a high temperature stable emulsifier, (ii) a low-end rheology modifier, (iii) a viscosifier with covalently linked organic groups, and (iv) a fluid loss control additive. Molecular architectural designs and synthesis of all four chemicals were carried out in our laboratory and used in optimum quantities to build industry's next generation invert emulsion fluids at density ranges from 75 – 135pcf (10-18ppg) and application temperature range of 60-450°F. Rheological and other important drilling fluid properties were tested at different downhole pressures and temperatures using a standard API recommended HTHP apparatus. The results demonstrated extreme thermal stability all the way from 60-450°F with excellent fluid loss control and ultrathin filter cake. The novel covalently-linked organophilic viscosifier used herein has proven superior thermal stability compared to existing organo-clay based systems especially at temperatures above 350°F. Novel secondary emulsifier and low-end rheology modifier have demonstrated excellent emulsion stability at temperatures up to 450°F. It has been an industry challenge to obtain true flat rheological behavior under high pressure and temperature using commercially available chemistries. However, very interestingly, fluids optimized in this work have exhibited excellent flat-rheological behavior for a wide range of temperatures. We will present a comparative analysis of the relationship between molecular structure and properties perspective of what is currently used in the industry versus those developed in this work. The current work has led to development of four novel chemical additives which are responsible for the industry's next generation high performance invert emulsion drilling fluids with flat-rheological behavior.

Sagging Prevention for Hematite-Based Invert Emulsion Mud

The solids sagging in high-pressure high-temperature (HP/HT) reservoirs is a common challenge associated with hematite drilling fluids. This study provides a solution to hematite sagging in invert emulsion mud for HP/HT wells which involves the combination of Micromax (Mn3O4) with hematite. The particles of both weighting agents were characterized to address their mineralogical features. A Field formulation of the mud was used over a range of Micromax/hematite ratios (0/100, 20/80, and 30/70%) in laboratory experiments to address the sag performance and determine the optimal combination ratio. Then, density, emulsion stability, rheology, viscoelasticity, and filtration performance for the formulated mud were addressed. The tests were conditioned to 500 psi and 350 °F. The acquired results of sag tests indicated that incorporation of 30% Micromax solved the hematite sagging issue and brought the sag tendency within the recommended safe range. An insignificant reduction in mud density was observed upon the inclusion of Micromax, while the emulsion stability was obviously improved from 551 to 614 volts with the 30% Micromax mixture. The recommended 30/70% combination had almost no effect on plastic viscosity and yield point since they were increased by one unit, but the gel strength was improved resulting in flat rheology and better solids suspension capacity. The filtration behavior of the formulation with 30% Micromax was enhanced compared to pure hematite as it resulted in 10 and 14% reduction of the filtrate volume and filter-cake thickness, respectively. This study contributes to improve and economize the drilling cost and time by formulating a stabilized and distinguished-performance drilling mud using combined weighting agents at HP/HT.

Use of Micronized Weighting Agents for High Density Completion Fluids: A Case Study

A unique invert emulsion fluid (IEF) weighted up with treated micronized weighting agent (MWA) slurries has been developed and successfully implemented in the field as a completion and testing fluid. The utilization of this unique IEF by design allowed the fluid properties to be lower on viscosity and superior suspension characteristics, which allowed for thermally stable fluid and provided excellent downhole hydraulics performance. Much of the earlier development and deployment of this type of IEF was focused on drilling for sections in narrow mud weight and fracture gradient windows, coiled tubing operations, managed pressure drilling, and extended reach wells. Many of these drilling challenges are also encountered in high pressure and high temperature (HTHP) and ultra-deepwater field developments and mature, depleted fields. Early fluid developments focused on designing the fluids chemistry and physics interactions and the optimization of mineralogy of the weighing agent used. There was also some concern on variability of the results seen on the return permeability as well as standard fluid loss experiments. The paper describes the laboratory and field and rigsite data generated while using the MWA in IEFs during completion operations with a client in India. The paper will briefly describe the laboratory work before the application and the associated results observed on the rig site. It will also outline all the challenges which were faced during the execution and mixing of the MWA IEFs. Each separate operation required a high-density reservoir fluid solution above 15.5 ppg [1.85 sg]. Because corrosion, sag potential, and scale were the operator's main concerns, a solids-free brine or other type of weighting agent (for e.g. Calcium Carbonate and/or Tri-Manganese Tetra Oxide) solution was not favored. A high-density IEF designed with MWA allowed us to provide a solution that mitigated against the risks identified in each operation. The thin viscosity profile enabled completion activities to proceed with minimal fluid consumption at surface, reducing the overall environmental impact. The high-density (15.6 ppg [1.86 SG] and 16.2 ppg [1.94 SG]) invert emulsion fluid was designed to minimize sag potential with minimal reservoir damage potential. With a thinner viscosity profile compared to conventional IEFs at equivalent densities, the fluid enabled completion activities with minimal fluid volumes lost over shakers and reduced the environmental impact. The MWA that was used to build the IEF used for drilling and completion fluid enabled maintenance of extremely low-shear rate viscosities when compared to conventional barite-laden fluids. This fluid was used for suspending and abandoning the well in Case Study A, where the reentry and intervention of the well was planned to be after 2 years. After exposure of the fluid in Case Study A, the fluid showed minimum sag after re-entry of the well and the intervention activities were done without any problems. Case Study B showed that the fluid was mixed to the density of 16.2 ppg and was used to perforate and test two different zones. The bottom hole static temperature (BHST) reported were 356 degF (180 degC) for Case Study A and 376 degF (191 degC) for Case Study B respectively. The paper attempts to show the effects of using this alternative weighing agent as a completion fluid instead of a high-density solids-free brine or other solids-laden high-density brines and the associated success, which could be managed if the fluid design is carefully planned.

Low ECD High Performance Invert Emulsion Drilling Fluids: Lab Development and Field Deployment

The present paper describes the results of the formulation of an acid-soluble low ECD organoclay-free invert emulsion drilling fluid formulated with acid soluble manganese tetroxide and a specially designed bridging package. The paper also presents a short summary of field applications to date. The novel, non-damaging fluid has superior rheology resulting in lower ECD, excellent suspension properties for effective hole cleaning and barite-sag resistance while also reducing the risk of stuck pipe in high over balance applications. 95pcf high performance invert emulsion fluid (HPIEF) was formulated using an engineered bridging package comprising of acid-soluble bridging agents and an acid-soluble weighting agent viz. manganese tetroxide. The paper describes the filtration and rheological properties of the HPIEF after hot rolling at 300oF. Different tests such as contamination testing, sag-factor analysis, high temperature-high pressure rheology measurements and filter-cake breaking studies at 300oF were performed on the HPIEF. The 95pcf fluid was also subjected to particle plugging experiments to determine the invasion characteristics and the non-damaging nature of the fluids. The 95pcf HPIEF exhibited optimal filtration properties at high overbalance conditions. The low PV values and rheological profile support low ECDs while drilling. The static aging tests performed on the 95pcf HPIEF resulted in a sag factor of less than 0.53, qualifying the inherent stability for expected downhole conditions. The HPIEF demonstrated resilience to contamination testing with negligible change in properties. Filter-cake breaking experiments performed using a specially designed breaker fluid system gave high filter-cake breaking efficiency. Return permeability studies were performed with the HPIEF against synthetic core material, results of which confirmed the non-damaging design of the fluid. The paper thus demonstrates the superior performance of the HPIEF in achieving the desired lab and field performance.