A.H. Hale

Transport in Shales and the Design of Improved Water-Based Shale Drilling Fluids

Transport of water and ions in shales and its impact on shale stability were studied to facilitate the improvement of water-based muds as shale drilling fluids. Transport parameters associated with flows driven by gradients in pressure and chemical potential were quantified in key laboratory and full-scale experiments. The experimental results show that the low-permeability matrices of intact, clay-rich shales can act as imperfect or leaky membranes that will sustain osmotic flow of water. Moreover, the ability of shales to act as osmotic membranes is shown to provide a powerful new means for stabilizing these rocks when exposed to water-based drilling fluids. Guidelines are presented for effective exploitation of shale membrane action and induced osmotic flows through optimized water-based drilling fluid formulation. In addition, special attention is given to induced electro-osmotic water flow in shales driven by electric potential gradients, which may provide an exciting, new, environmentally benign means for stabilizing shale formations.

Manipulation of Coupled Osmotic Flows for Stabilisation of Shales Exposed to Water-Based Drilling Fluids

Coupled osmotic flows have been studied as a means of stabilising shales exposed to water-based muds. The prime factor that governs the magnitude of chemical osmotic flow, i.e. the shale-fluid membrane efficiency, was investigated in detail. Its dependence on shale parameters, fluid parameters and external conditions was quantified. Membrane efficiency was found to increase with an increase in (hydrated) solute-to-pore-size ratio, with an increase in the shale`s high-surface area clay content and with a decrease shale permeability when increasing effective confining stress. Moreover, new drilling fluid chemistries for improving the efficiencies of low- and non-selective shale-fluid systems were identified. Induced osmotic flow with optimised shale-fluid membrane efficiencies in water-based environments is presented as a new strategy for improving wellbore stability in shales.

Hydrate plug remediation : Options and applications for deep water drilling operations

Gas hydrate formation during deep-water offshore drilling is a well-recognized operational hazard. Plugging the Blowout Preventor (BOP) stack, choke and kill lines with hydrates can cause a serious well control problem. In this paper, we examined the available options to remove a hydrate blockage from the choke and kill lines. The options included radial heat tracing, pipe warm-up, and hot water circulation through coiled tubing. A complete mathematical formulation of the energy balance of the hydrate melting process is presented. We examined the effects of heat flux, hydrostatic pressure over the plug, insulation thickness and quality, water circulation rate, and inlet water temperature on the melting process. The results showed that the controlling parameters are the heat flux, the quality of the insulation material, and the water circulation rate. The results also indicated that heat tracing is a viable technique to either melt a hydrate plug or to keep the choke and kill lines warm enough not to form hydrates. Furthermore, if coiled tubing intervention is permissible, hot water circulation can also be an effective method to remove hydrate blockages. In both cases, the choke and kill lines must be insulated. Otherwise, the heat losses to the environment will consume the bulk of the delivered energy.

Laboratory development and field application of a novel water-based drill-in fluid for geopressured horizontal wells

Research has identified a novel water-based drill-in fluid for drilling and completing geopressured horizontal wells. This fluid has a unique combination of properties which make it especially suitable for geopressured applications. They include the use of calcium and/or zinc bromide as a base brine, minimal concentration of calcium carbonate as bridging material, low plastic viscosity, tight fluid loss control, good filter cake properties, and excellent return permeability. This drill-in fluid has been used successfully to drill a 1,200 foot production interval, 4.75 inch diameter wellbore in the Gulf of Mexico with a system weight of 13.2 1bm/gal, bottom hole temperature of 185° F., and a 1400 to 1700 psi overbalance. The system functioned very well in both the drilling and completion operations. Fluid rheology was easily maintainable and the hole conditions were excellent without torque or drag problems. Initial production data suggests that the well is producing at expected rates with low drawdown pressure.

Bit Balling Reduction by Electro-Osmosis While Drilling Shale Using a Model BHA (Bottom Hole Assembly)

In this paper we present further work on the use of electro-osmosis to prevent bit-balling. Indentation tests in wet clay have indicated that the process of electro-osmosis (EO) becomes more efficient in clays with lower water content. This fundamental behavior of wet clay correlated well with coefficient of friction measurements under EO, between a rotating metallic cylinder and a stationary shale sample for different types of shales. Test results have demonstrated that shales with a higher water content (>10%) respond to EO to a smaller degree compared to shales with lower water content (<10%). Furthermore, in clay/sand mixtures it was clearly seen that the process of EO became active when the clay content exceeded a threshold value of about 10-12% by weight. This finding indicates that EO may be effective in sand/clay mixtures whereas until the present it has been believed to be effective only in clays. We have also conducted drilling studies using a model BHA (Bottom Hole Assembly) in which a stabilizer above the bit acts as the anode while the bit is cathodic. This self contained arrangement is preferred for practical application of the technology in deep wells. Drilling tests in Pierre shale using this equipment have shown increases in ROP (rate of penetration) of 30% in roller cone bits and up to 158% in the case of PDC bits when the bit was made negative, with substantially less cuttings adhering to the bit. The greatest increases in ROP were found at the higher weights on bit. The effects of EO increased progressively as the current density to the bit was increased.

Method to quantify viscosity effects on dispersion test improves testing of drilling-fluid polymers

Many of the available polymers are claimed to inhibit cuttings dispersion effectively. The experiments done to support these claims show the effectiveness of the polymers in inhibiting dispersion of sized shale through the hot rolling dispersion test. One of the most significant factors in this test is the viscosity of the test fluid. The fluid viscosity can create the illusion that a particular product effectively inhibits cuttings dispersion. In this paper a method is presented in which the dispersion-inhibiting effect of viscosity can be subtracted from the amount of shale retained to obtain a more accurate determination of the effectiveness of a drilling-fluid additive to inhibit cuttings dispersion. A comparison is presented that clearly demonstrates that the partially hydrolyzed polyacrylamide (PHPA) polymer is the best available polymer to inhibit cuttings dispersion cost-effectively.

Laboratory Development and Field Application of a Novel Water-Based Drill-In Fluid for Geopressured Horizontal Wells

Research has identified a novel water-based drill-in fluid for drilling and completing geopressured horizontal wells. This fluid has a unique combination of properties which make it especially suitable for geopressured applications. They include the use of calcium and/or zinc bromide as a base brine, minimal concentration of calcium carbonate as bridging material, low plastic viscosity, tight fluid loss control, good filter cake properties, and excellent return permeability. This drill-in fluid has been used successfully to drill a 1,200 foot production interval, 4.75 inch diameter wellbore in the Gulf of Mexico with a system weight of 13.2 lbm/gal, bottom hole temperature of 185{degrees} F., and a 1400 to 1700 psi overbalance. The system functioned very well in both the drilling and completion operations. Fluid rheology was easily maintainable and the hole conditions were excellent without torque or drag problems. Initial production data suggests that the well is producing at expected rates with low drawdown pressure.

Inhibition of gas hydrates in deepwater drilling

With the movement of offshore rigs into deep water, the problem of gas hydrates has become an important issue in drilling. If a kick is taken, gas hydrates can form in the blowout preventer (BOP) or chokelines while the kick is circulated out. The water-based pill presented here significantly improves gas-hydrate inhibition. This pill, which can be spotted in the BOP and weighted up, is environmentally safe and easily adaptable to offshore operations. Compatible with commonly used drilling fluids, the pill can be mixed directly into the mud system without any adverse effects after the danger of hydrate formation diminishes. This technology is an important safety consideration for deepwater drilling well control and hydrate-free operations above the mudline.

What price quality; Implementation of the API quality program for drilling-fluid materials

In 1985, the American Petroleum Inst. (API) issued the first edition of API Spec. Q1, which dealt with new certification procedures for equipment and materials. This paper discusses APIs Spec. Q1 program as it relates to drilling-fluid products and reveals the problems encountered when API Spec. 13A was modified.