FE 02-09 Intro to Drilling Fluids

Nội dung text: FE 02-09 Intro to Drilling Fluids

1. Circulatory System
2. Functions of Drilling Fluid 1. Remove drilled cuttings from the borehole 2. Carry and release the cuttings at the surface 3. Suspend cuttings and weight material in suspension when circulation is stopped 4. Release cuttings when processed by surface equipment 5. Allow cuttings to settle out at the surface
3. Functions of Drilling Fluid 10.Seal porous and permeable zones with an impermeable filter cake 11.Help support part of the weight of the drillstring/casing 12.Ensure maximum information from the formation drilled 13.Do everything, without damage to the circulation system or upon the formation adjacent to the hole
4. Mud Weight • MW must be sufficient to contain subsurface pressures and to prevent the formation from caving in • Not practical or economical to have the mud weight too high – Low ROP – Fracturing of weak formation -> lost circulation
5. Lost Circulation • The lack of drilling fluid returning to the surface after being pumped down a well • Due to: – Fissures, caverns, fractures – Enlarged hole size – Excessive mud weight • Terms used to describe degree of loss: – Seepage – Partial lost returns / circulation – Total lost returns / circulation
6. Gel Strength • Refers to the ability of the drilling fluid to develop a gel as soon as it stops moving • Determined with a Fann VG (Viscosity/Gel) Meter • Expressed in lbs/100ft2 • Its purpose is to suspend the cuttings and mud solids (weight material) in the borehole and not permit them to settle around the bit when circulation is halted • Gel strength should be low enough to – Allow the cuttings to be removed at the surface – Permit entrained gas to be removed at the surface – Minimize swabbing when the pipe is pulled from the borehole – Permit starting of circulation without high pump pressures
7. Water Loss • Control of the filtration rate (water loss) is necessary for two reasons: – A poor quality filter cake may cause excessive water loss and produce an excessively thick filter cake – High water loss can cause deep invasion of the formations, making it difficult to interpret wireline logs
8. Hydrostatic Pressure • The pressure that exists due to the mud weight and vertical depth of the column of fluid • The size and shape of the fluid column have no effect • Formula used: – Hp or P (psi) = 0.519 x MW (lbs/gal) x TVD (feet) – Hp or P (bars) = 0.0981 x MW (g/cc) x TVD (meters)
9. Equivalent Mud Weight • The mud weight that would exert a hydrostatic pressure equal to the sum of the imposed pressure and the hydrostatic pressure • Used interchangeably with Equivalent Circulating Density (ECD) • Calculated by DLS computer using Power Law • MWe = MWo + Pi/(0.0519 x TVD) – where, MWe = Equivalent MW; MWo = Original MW; Pi = imposed pressure
10. Types of Drilling Fluids • Water-based muds • Oil-based muds • Synthetic muds • Air, Gas, Mist systems
11. Non-Dispersed • Include spud muds, natural muds and other lightly treated systems generally used for shallow wells or top-hole drilling. • Thinners and dispersants are not added to disperse drill solids and clay particles.
12. Calcium-treated • High levels of soluble calcium are used to control sloughing shale and hole enlargement, and to prevent formation damage. • Hydrated lime (calcium hydroxide), gypsum (calcium sulfate) and calcium chloride are principal ingredients of calcium systems. • Calcium treated muds resist salt and anhydrite contamination but are susceptible to gelation and solidification at high temperatures.
13. Low Solids • Total solids should not range higher than about 6% to 10% by volume. Clay solids should be some 3% or less and exhibit a ratio of drilled solids to bentonite of less than 2:1. • Low solids systems typically use polymer additive as a viscosifier or bentonite extender and are non- dispersed. • One primary advantage of low-solids systems is that they significantly improve drilling penetration rate.
14. Components of a Water-Based Mud • Continuous liquid phase of water in which clay materials are suspended • Reactive solids • Inert solids
15. Water-Based Mud: Reactive Solids Component • Clays (“gel”) • Dispersants • Filtration Control Agents • Detergents, Emulsifiers and Lubricants • Defoamers • Sodium and Calcium compounds
16. Reactive Solids: Dispersants/Deflocculants • Reduce viscosity by adsorption onto clay particles, reducing flocculation • Also aid in filtration control since filtration problems are related to flocculation
17. Examples of Dispersants • Tannins (extracted from the quebracho and hemlock trees) • Phosphates (up to depths <175 F BHT) • Lignite • Lignosulphonates (obtained from spent sulfite liquor generated during paper manufacturing)
18. Reactive Solids: Detergents, Emulsifiers and Lubricants • Assist in cooling and lubricating • Also used for a spotting fluid in order to free stuck pipe
19. Reactive Solids: Sodium and Calcium Compounds • Sodium Compounds precipitate or suppress calcium or magnesium that decreases the yield of the clays. • Calcium Compounds inhibit formation clays and prevent them from hydrating or swelling.
20. Inert Solids: Weight Material • Finely ground, high-density minerals held in suspension to control mud density • Common weight materials are: – Barite – Hematite – Galena
21. Inert Solids: Anti-Friction Material • To reduce torque and decrease the possibility of differential sticking • More frequently it is used on high angle directional wells, where torque and differential sticking are a problem • Most frequently used materials are inert polyurethane spheres
22. Oil-Based Muds (EDIT 2) • Used for a variety of applications where fluid stability and inhibition are necessary, such as high- temperature wells, deep holes and where sticking and hole stabilization are problems. • Their high cost and difficulty of running, and complication of geological evaluation preclude their use on exploratory wells, other than in certain troublesome evaporite and clay sections
23. Emulsion (Oil/Water) System • Diesel or crude oil is dispersed in a continuous phase of water
24. Oil Muds • The IADC identifies oil muds as, “usually a mixture of diesel fuel and asphalt; not emulsions at the start of their use in drilling.
25. Synthetic Muds (SBM) • Synthetic fluids are designed to mirror oil- based mud performance, without the environmental hazards. • Primary types of synthetic fluids are esters, ethers, poly alpha olefins and isomerized alpha olefins. They are environmentally friendly, can be discharged offshore and are non-sheening and biodegradable.
26. Air Drilling • A compressor assembly including cooling system, air receiver and unloading system replaces the mud pump • The air line is connected to the swivel hose at the top of the kelly or top drive. • A small stream of water is often introduced into the air system to help cool the drill bit and control dust