Aqueous Drilling Fluids Research Articles

Influence of Clay Content and Surfactant on the Rheology of Non Aqueous Drilling Fluids

Organophilic clays are widely used in non-aqueousdrilling fluids, mixtures of different components being used in a well bore. As bentonite claysare not naturally organophilic, they can be modified by specific treatments with surfactants (ionic or nonionic). Recent studies demonstrate the influence of clay, surfactant,and the presence of a dispersant in the rheology of fluids. In this study we verified the influence of clay, and surfactant in the production of organophilic clays using an alcoholic route for the rheology of non-aqueous fluids.As such, we performed the characterization of organophilic clays by X-ray diffraction (XRD),these non-aqueous fluids were produced according to Petrobras norms for rheological testing. The results evidenced influences of the clay / surfactant ratio on the rheology of non-aqueous drilling fluids.

Experimental Investigations Into the Performance of a Flat-Rheology Water-Based Drilling Fluid

Summary The aqueous drilling fluid (AF) with unique flat rheology (FR), as a potential alternative to nonaqueous fluids (NAFs), is meaningful in deepwater operations. In this work, a novel FR water-based mud (WBM) was presented. An evaluation of FR profiles was conducted on the designed system by detecting the typical rheological data at a certain temperature and pressure range. The results showed that for the newly developed WBM, in addition to typical FR parameters [i.e., 6- and 3- rev/min readings and yield points (YPs)], the viscosity term also delivers near-constant variations in the temperature range of 39 to 150°F. To attain FR profiles, the rheological modifier appears to be necessary for its temperature-activated behavior. In addition, the FR WBM displays lower pressure and temperature dependence. The laboratory contamination tests indicated that the WBM system possesses excellent inhibition and lubricity properties as well as a strong tolerance to the contamination of seawater and sand/mudstone cuttings.

Simulation of Drilling Fluid Filtrate Invasion Near an Observation Well

Summary We used a commercial reservoir simulator to study, first, the dissipation of aqueous drilling fluid filtrate invasion around a cased observation well in an oil-saturated formation under the action of capillary pressure and, second, the interaction of a waterflood front with the cased well and remaining invaded zone. Hysteretic behavior of the capillary pressure and relative permeabilities is critically important to these processes and is taken into account by the use of the Carlson model, with the various bounding drainage and imbibition curves computed from a pore network model. Filtrate invasion into a hydrocarbon formation influences the readings of well-logging tools. Although this phenomenon has been known, and corrected for, for many years, uncertainty remains with regard to the long-time behavior of invasion around observation wells where no flow in or out of the formation occurs after completion, and with regard to the influence of formation wettability. We find that after sufficient time, the invaded zone dissipates completely in a water-wet formation, but some invasion always remains in the oil/mixed-wet case. Nonwetting-phase trapping, manifested through relative permeability hysteresis, is the cause. Because trapping affects the values and the endpoints of the relative permeability curves, a waterflood front passing across an observation well is more distorted in the oil/mixed-wet case. The simulation results allow us to understand how logging-tool measurements made in cased observation wells are influenced by drilling-fluid invasion and will therefore lead to improved interpretation. This study shows strong links between the wettability of the formation and the persistence of invaded zone saturation and between invaded zone saturation and the distortion of subsequent flood fronts.

Casing While Drilling (CwD): A New Approach To Drilling Fiqa Formation in the Sultanate of Oman—A Success Story

SummaryHighly reactive Fiqa shale used to compel well engineers in the Sultanate of Oman to plan drilling phase of surface and intermediate sections primarily based on time exposure to aqueous drilling fluid water-based mud (WBM). The new approach of drilling the time-dependent Fiqa formation using casing-while-drilling (CwD) allows well engineers to plan prospective top/intermediate wellbore sections differently by enhancing the overall drilling performance. This reduces the risk of setting casing strings at unplanned depths, getting pipe stuck, or reaming continuously when drilling with conventional drillstring. The technical feasibility study, risk assessment, planning, execution, and the lessons learned during the process of drilling two top-section pilot projects are described in this document. The CwD team compares the drilling performance of several offset wells and suggests actions to improve the CwD technology in Oman.Two 17½ - and 22-in. surface sections were drilled successfully with large-diameter casing strings and reached 754- and 894-m measured depths, respectively. The implementation of the CwD concept reduced the overall drill/case phase time up to 40%, in comparison with the average using conventional drilling in those fields. Exposure time of Fiqa to aqueous environment was reduced by eliminating conditioning trips and nonproductive-time (NPT) associated with wellbore instability. Drilling both sections with non-retrievable 17½×13⅜-in. and 22×18⅝ -in. CwD systems did not require modification of well design or rig. The optimization of this technology will support its implementation as the conventional drilling approach in some fields in Oman.

EVALUATION OF THE BEHAVIOR OF BIODEGRADABLE LUBRICANTS IN THE DIFFERENTIAL STICKING COEFFICIENT OF WATER BASED DRILLING FLUIDS

This work aims to evaluate the behavior of four samples of biodegradable lubricants in the differential sticking coefficient of aqueous drilling fluids. Eighteen formulations of fluids containing bentonite clay, lubricants and biodegradable polymers in different concentrations were studied. The experiment focused on observing the samples’ rheological properties, its filtration, the cake thickness, the lubricity coefficient, and, finally, the coefficient of the differential sticking. The results showed that the polymer additives improved rheological and filtration properties significantly. Also, the findings confirmed the idea that the presence of a lubricant leads to a reduction in lubricity, LC, and affects the differential sticking coefficient, DSC, of the fluids. However, the experiment observed a small variation on the LC as a result of an increase in the lubricant content. Overall, the results of the LC and the DSC of the fluids containing biodegradable lubricant additives were outstanding, being similar to the ones observed for oil-based fluids.

Penetration length studies of supercritical water jets submerged in a subcritical water environment using a novel optical Schlieren method

In hydrothermal spallation deep drilling a high-velocity, hot, supercritical water jet is directed towards the rock to induce fragmentation. One major challenge in the realization of this novel technique is the entrainment of comparatively cool, aqueous drilling fluid by the hot water jet, which can lead to significant heat losses before the hot jet's energy can be transferred to the rock. The present work quantifies such entrainment effects by determining penetration lengths of supercritical water jets injected into a cool, subcritical environment using a novel optical Schlieren method. Penetration lengths of supercritical jets were found to be equal to the injector's nozzle diameter and almost independent of the jet's temperature at the nozzle exit and the jet's mass flow under almost all experimental conditions investigated. A semi-empirical model adapted from steam jet studies confirmed these findings and indicates that heat and mass transfer are primarily controlled by turbulent mixing.

Effect of non-aqueous drilling fluid and its synthetic base oil on soil health as indicated by its dehydrogenase activity

Drilling fluids are used for drilling natural gas, oil and water wells. These spill over into the surrounding soil at the point of drilling, which may impair soil health. A laboratory investigation was carried out to determine the effect of non aqueous drilling fluid (NADF) and synthetic base oil used with it on soil health as indicated by the dehydrogenase activity. A non-sterile sandy loam soil was treated with different amounts of NADF and base oil at a rate of 800, 8,000 and 16,000 mg kg−1. Initially, reduction in dehydrogenase activity was observed, but it increased with the incubation time. On the 60th day of incubation dehydrogenase activity in untreated control was 1.04 mg TPF g−1 h−1 whereas in the soil samples treated with NADF and the base oil (16,000 mg kg−1), the activity was 1.53 mg TPF h−1 and 1.90 mg TPF h−1, respectively, which was 72 and 82% more than in untreated control. Base oil-treated soil showed more dehydrogenase activity than that observed with NADF. Both NADF and base oil stimulated the soil dehydrogenase activity.

Fractal characteristics of granularity distributions of aqueous bentonite and bentonite–polymer muds

In order to explore the possibility of characterizing quantitatively the granularity distributions of dispersed clay particles in aqueous drilling fluids, the fractal approach was used to analyze the granularity distribution data for various bentonite and bentonite–polymer muds. It is found that these granularity distributions are characteristic of fractal nature and their inhomogeneity can be measured by the fractal dimensions. Depending on the composition of the muds and treatment conditions, various fractal dimensions were obtained and discussed.

Zirconium Additives for High-Temperature Rheology Control of Dispersed Muds

Summary Environmental considerations have stimulated new interest in the use of aqueous drilling fluids in situations where oil-based muds have previously been preferred. The least expensive and most widely used aqueous drilling fluids are dispersed muds made up with bentonite clay. These bentonite muds, however, possess limited rheological stability at elevated temperature and are also often formulated with chromium-containing thinners that are increasingly subject to environmental regulation. This paper describes a new zirconium-based rheology control additive of low toxicity that is extremely effective at extending the rheological stability of both chromium-containing and chromium-free bentonite muds at high temperature. The results of mud-aging experiments carried out between 150 and 200°C on both laboratory and field-conditioned bentonite muds illustrate the rheology-stabilizing characteristics of this additive. The low cost of drilling fluids formulated with the zirconium additive makes them attractive candidates for resolving the environmental issues and limited rheological stability of existing bentonite muds.

A New Chrome-Free Lignosulfonate Thinner: Performance Without Environmental Concerns

Summary Chrome-free lignosulfonates are increasingly used in aqueous drilling fluids because of potential environmental concerns associated with the chromium counterparts. A basic design study of a chrome-free lignosulfonate showed three major reaction parameters affecting its performance: type and concentration of complexed metal ion, oxidation level under optimal pH, and lignosulfonate raw liquor. A new chrome-free lignosulfonate formulation based on titanium metal ion was developed and its plant scale-up was conducted. Testing of the new titanium-complexed lignosulfonate was found to give improved rheological control vs. other available chrome-free lignosulfonates in various water-based drilling fluid applications.

A New Method for the Quantitative Determination of Soluble Carbonates in Water-Based Drilling Fluids

This paper presents a new, direct method for measuring soluble carbonates in a drilling fluid. The method is designed primarily for field use in guiding mud treatments and controlling adverse mud rheology. Laboratory data are given to verify the method's accuracy and field experience illustrates its usefulness in mud control. Introduction The mechanism by which bicarbonate (HCO3-) and carbonate (CO3=) ions adversely affect a deflocculated, clay-based drilling mud's performance (and even these ions' true concentrations) has been a controversial point in the industry for many years. Under field analysis conditions, only an estimate of carbonate concentration in filtrate samples is obtained by API alkalinity titrations. Even under ideal laboratory conditions, alkalinity titrations only approximate the true carbonate content of complex muds.However, a reliable method that allows direct carbonate analysis of muds recently was developed. The Garrett Gas Train/Carbonate (GGT/CO3=) method determines total soluble carbonates as gaseous CO2, freed from the sample upon acidification in a small, transparent, plastic gas train. The evolved CO2 is measured quantitatively using a commercial gas detector tube. The GGT/CO3 = method was developed with the same concept as the GGT/S= method for measuring sulfides, which recently was adopted as an API permanent procedure. The similar chemical behavior of the CO2 -carbonate and H2S-sulfide systems in aqueous solutions allows analogous approaches to quantitative analyses and chemical treatment. Although alike in many ways, the gas-train/detector-tube analysis method for carbonates is more restrictive and sensitive to detector-tube flow conditions than is sulfide analysis. These conditions are specified later when the procedure is described.Uses for GGT/CO3 = analyses go beyond the main application for measuring and treating accumulated carbonates in field muds and includestudying carbonate generation rates caused by thermal degradation of organic additives that produce CO2 in muds (such as lignites, lignosulfonates, carboxymethyl cellulose, tannins, and starches),studying the rate of CO2 absorption from air into a circulating mud when influenced by various equipment used to process muds,analyzing soluble carbonates in commercial barite to determine if soda ash or sodium bicarbonate are present,studying the chemical reaction efficiency between carbonates and a given treatment material such as lime - especially useful for field and laboratory pilot tests of problem muds, andmonitoring accumulation of bacterially and chemically produced CO2 in packer muds, ballast muds for ships, and muds stored in tanks. Carbonate Chemistry in Water-Based Muds In alkaline, aqueous drilling or workover fluids, soluble carbonates are likely to accumulate from a wide variety of CO2 sources. Regardless of the source, if CO2, is generated internally or enters the mud externally, it reacts immediately with alkaline hydroxyl ions (OH) to form HCO3- and CO3 = ions. A chemical equilibrium is established at a given temperature, which is controlled by the H+ and OH- ion concentration or mud pH. These equilibria involve the component shown in Eqs. 1 and 2. (1) JPT P. 860