Nicholas Takach

Stability of Natural Gas in the Deep Subsurface: Thermodynamic Calculation of Equilibrium Compositions

The deepest hole in a sedimentary section is currently 31,441 ft (9,583 m), but the deepest production is only 26,536 ft (8,088 m); the depth gap between deepest hole and deepest producer is the largest in the history of the petroleum industry. This prompts a critical reevaluation of methane stability in deep potential reservoirs. We developed a computer program to calculate the equilibrium composition of gases in deep reservoirs of various lithologies. The program establishes the assemblage with minimum free energy for specified conditions of temperature and pressure corresponding to conditions down to 40,000 ft (12,192 m) and can handle up to 70 components, 25 elements, and 20 phases. It does not assume ideal gas behavior but does assume ideal mixing. Calculations have been made for average, high, and low geothermal gradients; hydrostatic and lithostatic pressures; and with and without graphite. Calculated equilibrium compositions show that methane alone in an inert reservoir has considerable stability, and 99.4% survives to 40,000 ft (12,192 m). Even in the geologically more realistic system with water, 99.1 survives. The full capability of the program is demonstrated for a sandstone reservoir with graphite, calcite cement, and a range of minor minerals. There, methane shows considerable stability for average geothermal gradients with both normal and abnormal pressures. For high geothermal gradients, part of the methane is lost by reaction, and significant amounts of carbon dioxide are added to give a gas composition at 40,000 ft (12,192 m) that contains only 9% methane. The program shows that, in general, temperature is much more important than pressure in controlling gas composition, crude oil is not thermodynamically stable at any depth, and a few percent of hydrogen is frequently present in deep gases.

Pressure Profile in Annulus: Solids Play a Significant Role

This paper looks into the effects of solids on the wellbore pressure profile under different conditions. An extensive number of experiments were conducted on a 90-ft-long, 4.5 in. 8 in. full-scale flow loop to simulate field conditions. The flow configurations are analyzed. A solid–liquid two-phase flow configuration map is proposed. Significant difference is found between the pressure profile with solids and without solids in the wellbore. The results of this study show how the pressure profile in the wellbore varies when solids present in the annulus, which may have important applications in drilling operations. [DOI: 10.1115/1.4030845]

Sensitivity Analysis of Major Drilling Parameters on Cuttings Transport during Drilling Highly-inclined Wells

Abstract In this study, a layered cuttings transport model is developed for high-angle and horizontal wells, which can be used for incompressible non-Newtonian fluids as well as compressible non-Newtonian fluids (i.e., foams). The effects of major drilling parameters, such as flow rate, rate of penetration, fluid density, viscosity, gas ratio, cuttings size, cuttings density, wellbore inclination and eccentricity of the drillsting on cuttings transport efficiency are analyzed. The major findings from this study are, the dominating parameter on wellbore cleaning is the flow rate, and, as the viscosity of the fluid is increased, the thickness of the cuttings bed developed in the wellbore is significantly increasing. Also, cuttings properties, fluid density, wellbore inclination and eccentricity have some influence on cuttings transport.

Determination of Cuttings Lag in Horizontal and Deviated Wells

A literature review, preliminary modeling, preliminary experimental work and recent development of this project are presented in this report. The literature review has been focused on cuttings transport in horizontal and slightly inclined well-bores, solidliquid flow patterns (two and three layer models), particle slip velocity and particle tracking. To model the phenomena, correlations developed by Larsen, Iyoho 12 and Chien were used to calculate the particle traveling velocity, and then it was used to associate the particles with their original location using other relationships. Preliminary experimental work has been completed using the Low Pressure Ambient Temperature Flow Loop (L.P.A.T.) and a high speed camera. Due to a recent development the current report includes a suggested modification of the flow loop in order to record the bed height in the inclined condition.

Chemically improved filter cakes for drilling wells

Blast furnace slag (BFS) is a latent hydraulic material similar in composition to Portland cement. BFS was originally studied for mud to cement (MTC) purposes. This application called for large quantities of BFS (40-500 ppb (lb/bbl)) and ultimately proved to be ineffective. Subsequently, BFS has been investigated as an additive in drilling fluids. In a recent study, muds containing additive-level concentrations (5-30 lb/bbl) of BFS were shown to be effective in reducing formation damage. The present work extends the investigation of BFS as a drilling fluid additive. Specifically, we have explored the use of chemical reagents to activate the BFS in filter cakes to achieve cakes that are thin, impervious and firm. Filter cakes were formed from slag-laden drilling fluids in a high-pressure, high-temperature reverse filtration apparatus (permeability plugging apparatus). Studies were conducted with partially hydrolyzed polyacrlyamide (PHPA) muds and CaCO 3 -based fluids containing different loadings of BFS. Filter cakes of these fluids were treated with several different activators and the results were compared to cakes containing no BFS. Different activation techniques were investigated and a novel device was designed to measure the strength of the filter cakes. An environmental scanning electron microscope examined the relationship between the structural features of the activated cakes and their strengths. This study demonstrates that filter cakes containing BFS can be chemically activated to produce thin, firm cakes with improved filtration properties. These cakes should be able to form better bonds with cement subsequently used for completion.

Investigation of drilling fluids containing blast furnace slag for their potential impact on formation damage: A laboratory study

This work discusses the effect of incorporating blast furnace slag (BFS) as an additive in water-based drilling fluids. The intent of this treatment is rapid development of a thin, impervious, and easily removable filter cake, thereby minimizing detrimental impact of the drilling fluid on formation productivity as opposed to previous applications of BFS in universal fluids. To evaluate the impact of BFS on filter cake properties, permeability plugging apparatus (PPA) tests and dynamic formation damage (DFD) studies were conducted. Drill-in fluids and dispersed muds were tested using varying quantities of BFS. Once a steady rate of dynamic filter cake deposition was achieved, the BFS in the filter cakes was chemically activated. The results obtained from these activation studies were compared with those obtained with no BFS and with unactivated BFS. The nature of the filter cakes was examined with an environmental scanning electron microscope (ESEM). Results obtained from the PPA tests indicate substantial decreases in initial spurt loss and filtrate volume with increasing concentration of BFS. The DFD studies substantiate the. aforementioned observations and show enhancement of return permeabilities with BFS activation. ESEM studies demonstrate that BFS can consolidate filter cakes.

Density and Drag Reduction With Hollow Glass Additives

This study concentrates on the use of materials known as hollow glass spheres, also known as glass bubbles, to reduce the drilling fluid density below the base fluid density without introducing a compressible phase to the wellbore. Four types of lightweight glass spheres with different physical properties were tested for their impact on rheological behavior, density reduction effect, survival ratio at elevated pressures and hydraulic drag reduction effect when mixed with water based fluids. A Fann75 HPHT viscometer and a flow loop were used for the experiments. Results show that glass spheres successfully reduce the density of the base drilling fluid while maintaining an average of 0.93 survival ratio, the rheological behavior of the tested fluids at elevated concentrations of glass bubbles is similar to the rheological behavior of conventional drilling fluids and hydraulic drag reduction is present up to certain concentrations. All results were integrated into hydraulics calculations for a wellbore scenario that accounts for the effect of temperature and pressure on rheological properties, as well as the effect of glass bubble concentration on mud temperature distribution along the wellbore. The effect of drag reduction was also considered in the calculations.Copyright

Hydraulics of Drilling With Aerated Muds Under Simulated Borehole Conditions

Maintaining optimum circulation rates is important in aerated mud drilling operations. However, reliable predictions of the optimum rates require accurate modeling of the frictional pressure loss at bottom-hole conditions. This paper presents a mechanistic model for underbalanced drilling with aerated muds. Extensive experiments in a unique field-scale high pressure and high temperature flow loop were performed to verify the predictions of the model. This flow loop has a 150×89 mm2(6″×3.5″) horizontal annular geometry and is 22 m long. In the experiments, cuttings were introduced at a rate of 7.5 kg/min, representing a penetration rate of 15 m/h in the annular test section. The liquid phase flow rates were in the range of 0.30–0.57 m3/min, representing superficial liquid velocities in the range of 0.47–0.90 m/s. The gas liquid ratio (gas volume fraction under in situ condition) was varied from 0.0 to 0.38. Test pressures and temperatures ranged from 1.28 to 3.45 MPa, and 27°C to 80°C, respectively. Gas liquid ratios were chosen to simulate practical gas liquid ratios under downhole conditions. For all the test runs, pressure drop and cuttings bed height over the entire annular section were measured. Flow patterns were identified by visual observations through a view port. The hydraulic model determines the flow pattern and predicts frictional pressure losses in a horizontal concentric annulus. The influences of the gas liquid ratio and other flow parameters on the frictional pressure loss are analyzed using this model. Comparisons between the model predictions and experimental measurements show a satisfactory agreement. The present model is useful for the design of underbalanced drilling applications in a horizontal wellbore.

Investigation of Blast Furnace Slag Addition to Water-Based Drilling Fluids for Reduction of Drilling Fluid Invasion into Permeable Formations

Granulated quick-quenched blast furnace slag (BFS or slag) in water-based drilling mud systems has been studied before, mainly from the perspective of mud-to-cement (MTC) conversion. However, the concept of using slag in a drilling mud for an effective low permeability filter cake, which minimizes formation damage, has not been explored. This work explores the potential of using slag to consolidate filter cakes, thereby achieving reduced filter cake permeability. Also investigated is the overall impact on the reduction in formation damage by selective activation of BFS in dynamically deposited filter cakes. Studies were conducted on lignosulfonate, partially hydrolysed polyacrylamide (PHPA) and CaCO 3 Drill-In fluids with BFS as a mud additive. Various mud properties, such as rheology (ambient as well as high pressure/high temperature), pH, filtrate loss and initial spurt loss are reported for muds containing variable loadings of BFS, and a control containing no BFS. This study demonstrates the possibility of reducing invasion of mud into permeable formations through addition of small quantities of BFS to drilling mud. BFS appears to produce a more consolidated filter cake, which can be very useful for reducing wellbore stabilization problems in formation intervals that exhibit lost circulation and poor zonal isolation. In some cases BFS-containing drilling fluid appear to reduce formation damage in the near -wellbore environment.

Development of a New Diagnostic Method for Lost Circulation in Directional Wells

Failure to manage and minimize lost circulation can greatly increase the cost of drilling and the risk of well abandonment. Many lost circulation remedial procedures are not working as planned because the locations of loss zones are incorrectly estimated. The lack of this critical piece of information prevents treatments from being applied directly to the points of losses and, thus, resulting in low efficiency and extended NPT (non-productive time). This paper presents an integrated method for identifying the locations of loss zones with continuous temperature measurement data enabled by drilling microchip technology. A transient thermal model in predicting the temperature profiles in the wellbore and formation during mud loss is developed as a forward calculation procedure of the loss zone mapping method. For a deep well with moderate to severe loss, there are significant changes in the mud circulating temperature profiles as mud loss persists. Certain characteristics of wellbore thermal behavior are evaluated and identified as good indicators of loss zones. Case studies are conducted to demonstrate the practical applications of the method in both onshore and offshore drilling applications. The results from these case studies are important in setting cement plugs, applying expandable tubular systems, and spotting LCM (lost circulation material) pills. Additional uses of this method include identifying highly permeable zones for reservoir or formation evaluation purposes. This method can be used as a routine monitoring process performed regularly without any interference of the drilling operations at the time.