Oil and Gas Technology Program Oil and Gas Technology Program PTRT 1321 Oil-Field Hydraulics Chapter 1 Completion and Workover

Oil and Gas Technology Program Completion and Workover Completion – preparing a well to produce oil or gas. – Establish one or more flow paths in a well for production of reservoir fluids Workover – any operation performed on a well to restore or increase production. – Control water – Repair mechanical problems – Reservoir stimulation

Oil and Gas Technology Program Static Conditions in well Oil Water

Oil and Gas Technology Program Reasons for Workover Controlling water production or gas production Circumvent water coning Repair mechanical problems Stimulate reservoirs and increase production Recompletion in new reservoir or additional reservoir

Oil and Gas Technology Program Specific jobs for Workover Drill stem testing Perforating Fracturing Squeeze cementing Acidizing Sand control Plugging back Plugging and abandonment

Oil and Gas Technology Program Controlling water or gas production As oil is produced the gas-oil or oil-water interface changes Water production usually comes from deepest parts of reservoir so plugging back and recompletion may be in order Gas production may require deepening and recompletion

Oil and Gas Technology Program Why is this an issue? Gas production in an oil well uses up valuable reservoir energy that is needed to bring fluids to the surface Water production can cause: – Excessive corrosion – Sand production leading to erosion of equipment and plugging

Oil and Gas Technology Program Preventing Water Coning Reservoir normally oil-wet in areas containing oil – pores are coated with oil Excess production rates allows water to enter the well bore – becomes water wet Water wet allows water to flow more easily – results in more water wet areas Reduce production to correct OR plug pack and recomplete.

Oil and Gas Technology Program Static Conditions in well Oil Water

Oil and Gas Technology Program Low Production Conditions Oil Water

Oil and Gas Technology Program High Production Conditions Oil Water

Oil and Gas Technology Program Recompleting well Oil Water

Oil and Gas Technology Program Workover Operations Drill stem testing Perforating Fracturing Squeeze cementing Acidizing Sand control Plugging back Plugging and abandonment

Oil and Gas Technology Program Drill Stem Test (DST) Temporary completion to determine productivity of a zone and estimate size In cased well: – Isolate zone with packer – Open surface-operated valve allows formation fluids to flow into work string – Close valve and monitor BHP from which reservoir size can be determined – Regulations require DST string to be reverse-circulated prior to removal – Water cushion can be used to reduce hydrostatic head and improve initial flow of formation fluids. WC ft (height in feet) = P d (BHP) / FW(fluid lbs/gal) / (Note: Fresh water = 8.33 lbs/gal)

Oil and Gas Technology Program Example Calculation BHP = 2,852 psi at formation depth of 10,000 ft 200 psi differential required for well to begin flowing. Water cushion must be 2, = 2,652 psi Using 8.5 ppg salt water the height of the water cushion must be: WC ft = 2,652/8.5/0.052 = 6,000 ft For 2 7/8” tubing (capacity of bbl/ft) this amounts to: x6000 = bbl.

Oil and Gas Technology Program Workover Operations Drill stem testing Perforating Fracturing Squeeze cementing Acidizing Sand control Plugging back Plugging and abandonment

Oil and Gas Technology Program Perforating Jet charges (shaped charges) used to place hole into casing adjacent to producing zone. Wireline or tubing conveyed Expendable or retrievable or both Underbalanced pressure – Assists in removal of debris from perfs – Some possibility of sanding API RP-67 safety document.

Oil and Gas Technology Program

Oil and Gas Technology Program Workover Operations Drill stem testing Perforating Fracturing Squeeze cementing Acidizing Sand control Plugging back Plugging and abandonment

Oil and Gas Technology Program Fracturing Pumping fluid into well until producing formation cracks (fractures). Proppants are used to hold (prop) open these fractures. Typical fractures are orientated vertically and extend in two opposite directions away from the wellbore. Salt water is usually adequate to transport the proppant. Proppant should be round with little or no fines present Fracture pressures are achieved by using high pumping volumes (rate).

Oil and Gas Technology Program

Oil and Gas Technology Program Safety Precautions Contingency plans SPCC – Spill Control Plan Proper PPE Communications Emergency First Aid Evacuation Plans

Oil and Gas Technology Program Workover Operations Drill stem testing Perforating Fracturing Squeeze cementing Acidizing Sand control Plugging back Plugging and abandonment

Oil and Gas Technology Program Squeeze cementing Cement “squeezed” into perforations to: – exclude water or gas from the well. – Correct deficiencies in primary cementing job – Allows new zone to be recompleted – Repair corroded or damaged casing Also referred to as remedial or secondary cementing Covered further in PTRT 1307 Chapter 7

Oil and Gas Technology Program Variety of places to place the cement – Against formation in open hole – Pumped through perforations to contact formation Clean surfaces and open channels are important – Improved bonding – Ensure adequate flow Each squeeze job is unique and the cement must be selected specific for the task

Oil and Gas Technology Program Squeeze tool run in on work string – Drill pipe or tubing – Packer, when set, isolates the casing from the high pressure Pressure control critical – Avoid formation damage – Avoid “flash set” of cement Excess cement is reversed out of the well – Typical circulation is down the work string and then up the casing annulus.

Oil and Gas Technology Program Methods of Squeeze Cementing Bradenhead (Casing head) – No packer or squeeze tool in the hole Bullhead – Starting fluid in the string pumped into formation Hesitation – Pumps started and stopped during process until desired pressure is achieved Set-through – Excess cement in casing is washed out (special low water-loss cement is required) High or low pressure – High pressure no longer recommended due to potential for formation damage Circulation – Perforations placed above and below the zone – Retainer set between the perfs and circulation is established

Oil and Gas Technology Program Workover Operations Drill stem testing Perforating Fracturing Squeeze cementing Acidizing Sand control Plugging back Plugging and abandonment

Oil and Gas Technology Program Acidizing High solids content muds and excessive hydrostatic pressure can damage formation Pumping acids into formation can repair some or all of this damage. Some formations (limestone, dolomite) can have improved permeability by acidizing. Specific details are required to select proper conditions and acids for the job. Can be obtained by core analysis and logging

Oil and Gas Technology Program Repairing formation damage Typically occurs near the well bore. Acidizing should be performed at pressures below the fracture (breakdown) pressure of the formation Avoiding fracture keeps acid near the well bore while they work. Matrix acidizing

Oil and Gas Technology Program Acid fracturing Use when formation lacks permeability Dissolves some of the formation bedding material. Exercise caution in formations which also contain moveable water. Fractures produce vertical pathways for water which can produce excess water in the well bore.

Oil and Gas Technology Program Types of acids used HCl - Hydrochloric Acid (Muriatic acid) (most commonly used) HF – Hydroflouric Acid (highly dangerous) CH 3 COOH – Acetic Acid (Vinegar) HCOOH – Formic Acid (ants) Surfactant and corrosion inhibitors also used in conjunction with acids

Oil and Gas Technology Program Open hole Perforated casing

Oil and Gas Technology Program Safety practices Only use steel reinforced hoses On-site wash stations Pressure test all lines prior to using acids Tie down all lines and install working pressure guages Install check valve at well head (every check valve needs a tee and valve for pressure relief. Acid into water NOT the reverse. Avoid breathing fumes Proper PPE and monitor wind direction Pre-job safety meeting and on-site first aid certification

Oil and Gas Technology Program Workover Operations Squeeze cementing Perforating Drill stem testing Acidizing Sand control Fracturing Plugging back Plugging and abandonment

Oil and Gas Technology Program Sand control Can be a major problem – Cut or plug choke (see example) and flow lines – Excessive wear – Complicate well clean out – Malfunctions of down-hole equipment Control with – Screens or slotted liners – Gravel pack – Consolidation using plastic resins

Oil and Gas Technology Program

Oil and Gas Technology Program

Oil and Gas Technology Program Workover Operations Drill stem testing Perforating Fracturing Squeeze cementing Acidizing Sand control Plugging back Plugging and abandonment

Oil and Gas Technology Program Plugging Back Kill the well – fluids down wellbore so that hydrostatic pressure exceeds formation pressure Squeeze old perforations Often an old packer is used as a plug above the squeeze – regs sometimes require additional cement plug above the packer Retrievable packer or squeeze tool also can be used.

Oil and Gas Technology Program

Oil and Gas Technology Program Workover Operations Drill stem testing Perforating Fracturing Squeeze cementing Acidizing Sand control Plugging back Plugging and abandonment

Oil and Gas Technology Program Reasons to Plug and Abandon Possible casing deterioration Potential migration of fluids between zones Potential contamination of fresh water zones Blow out potential Offshore navigation hazards Regulatory requirement

Oil and Gas Technology Program Good Plugging and abandonment Squeeze cement the producing perforations Install cement plugs in casing as tubing or work string is pulled from the hole Often the upper un-cemented sections of casing can be cut off and recovered followed by cement plugs set in upper area of the hole. Removal of the well head

Oil and Gas Technology Program Completions Tubingless open-hole Tubingless cased-hole Conventional completion Multiple completion – Dual – interval – triple

Oil and Gas Technology Program Tubingless open-hole Casing set and cemented above the top of the pay zone No casing nor cement set opposite the producing formation No tubing in the well Perforations not usually necessary (hard formations may benefit) Perforated or slotted liner easily installed if sand control needed

Oil and Gas Technology Program

Oil and Gas Technology Program Disadvantages Well may require frequent clean out Well treatment can be difficult Casing is subject to corrosion by formation fluids Saltwater production may be difficult to control Stimulation of selected area is almost impossible

Oil and Gas Technology Program Tubingless cased-hole Production flow is through the casing (or liner) No tubing in hole Little flow restriction and easily deepened Well cleanout is easier than open hole Saltwater production is easier to control Selective stimulation of the formation is possible

Oil and Gas Technology Program

Oil and Gas Technology Program Disadvantages Cement may cause reduced production Gravel packing is more difficult through perforations Corrosion of casing is still a difficulty Perforation is required Log evaluation and correlation are essential Pressures are limited to casing strength

Oil and Gas Technology Program Conventional completion Most common type Perforated casing set and cemented through the pay zone Packer made up in tubing string and set above the production zone Tubing controls casing corrosion Higher pressures can be tolerated

Oil and Gas Technology Program Oil Water

Oil and Gas Technology Program Disadvantages Tubing restricts flow of produced fluids More expensive completion Advantages typically outweigh the disadvantages

Oil and Gas Technology Program Two-pay interval completionDual completion

Oil and Gas Technology Program Multiple completion Packers Casing Shoe Perforations

Oil and Gas Technology Program Pumping Well Completions Most wells will eventually need some form of artificial lift to maintain production rate Sucker rod pumping very common Used when natural flow due to formation pressure is no longer sufficient. Electric submersible pumps (ESPs) and down hole hydraulic pumps are an alternative using similar completion

Oil and Gas Technology Program Gas Lift Completions Casing set and perforated Packer run in above the producing interval Tubing with gas lift mandrels that hold gas lift valves is run in. Gas injected down the casing and enters the tubing through the gas lift valves Reduced density and viscosity allows production of reservoir fluids. Recovered gas is compressed and recirculated.

Oil and Gas Technology Program

Oil and Gas Technology Program Other types of completions Open tubing-and-casing – Minimal flow restriction – ID of tubing and casing exposed to corrosion – Pressure limited to casing bursting pressure Corrosive High-pressure – Small diameter kill string inside tubing – Easy to apply anti-corrosion or other chemicals Dual-string single – Extremely high pressure well – Running or pulling tubing is more time consuming – Either tubing string can be used for flow or chemical applications

Oil and Gas Technology Program Corrosive High-pressure Dual-string Single

Oil and Gas Technology Program Pump-Down (TFL) Completions Through flow-line (TFL) pumpdown equipment Conveyed down hole by fluid pumping Five basic parts – Pump to provide surface power – Circulation fluid – Suitable conduit – H-member to complete the circulation path – Tool string to perform the needed service