Novel Drilling Fluid for Through-Tubing Rotary Drilling

Abstract

fax 01-972-952-9435. AbstractThrough-Tubing Rotary Drilling (TTRD) is a technique which has been developed to extend the production life of older fields by substantially reducing drilling costs to render smaller reserves of oil economically recoverable 1 . However, the small wellbore dimensions required to utilise drill-pipe inside production tubing place some unusual demands on the drilling fluid and when these are compounded by the challenges of drilling into a formation containing a large range of pressures in the reservoir and high pressure shales, a radical approach to drilling fluid design is required.The requirement for a low viscosity fluid (to minimise ECD) which would still meet all other drilling requirements meant that conventional fluids were all unsuitable and a review of the options available resulted in the selection of a novel weighting material, manganese tetraoxide, for use in a mineral oil-based mud as the system most likely to provide the desired properties. The physical properties of commercially available manganese tetraoxide (very small, spherical particles) were known to result in very low plastic viscosities in muds made with this material when compared to muds weighted with barium sulphate. A much-reduced potential for weight material sag was an added bonus.This paper details the design considerations of the fluid used to drill three TTRD side-track wells in Shell's North Cormorant field. Modelling of hydraulic parameters is presented, together with field results from the first well and how these led to modifications of fluid design and engineering practice which were incorporated into the subsequent wells.

Formation Damage Induced by Various Water-Based Fluids Used to Drill HP/HT Wells

“…Field applications of the oil-based drill-in fluid utilizing Mn 3 O 4 showed maximum expected production and formation damage was not significant. 8 The use of Mn 3 O 4 weighting solid in water-based drill-in fluids might lead to good results similar to the oil-based drill-in fluids application. Therefore, this study will investigate water-based drill-in fluids using Mn 3 O 4 particles as weighting materials.…”

“…The low plastic viscosity associated with Mn 3 O 4 was a result of lower friction in particle to particle interaction due to their spherical shape. 8 Mn 3 O 4 was used with potassium formate brine to drill Gultakes reservoir. Gultakes reservoir has high permeability and small difference between pore pressure and fracturing reservoirs.…”

Managed-Pressure Drilling; Techniques and Options for Improving Efficiency, Operability, and Well Safety in Subsea TTRD

“…• Low ECD (achieved through low viscosity) • Low solids settling tendency (achieved through high viscosity) Two major drilling fluid service companies have solved these requirements differently, but the results are the same; by applying weight material with small particle size both rheology and sagging tendency have been improved compared with conventional mud systems 6,7 . Formate mud, where density is achieved through soluble salts and not through solids is an attractive alternative but its high cost may limit its application 8 .…”

Water-Based Drilling Fluid for HP/HT Applications

“…Manganese tetroxide has been used in several drilling operations where advantage was taken of its fine particle size to formulate fluids with relatively low rheology for TTRD (through tubing rotary drilling) applications. 4,5,6 The rheological properties of the above polymers, when dissolved in fresh water, were investigated by Gemma et al 7 They examined the effects at concentrations that would be used in a fully formulated drilling fluid. They observed that polyvinylpyrrolidone, when used on its own, has a weak viscosifying effect with a Newtonian character.…”