Cbm - Ppt.pptx

OVERVIEW OF CBM & IT’S WORKOVER OPERATIONS

ABSTRACT • Currently, gas demand exceeds supply by 30%, While the demand for natural gas in India is 118 million metric standard cubic meter per day (MMSCMD). The current supply from various sources is 90 MMSCMD, Leaving a shortfall of 28 MMSCMD. That deficiency can be covered by CBM production.

WHAT IS COAL BED METHANE ? • Standard Natural Gas C𝐻4 • CBM is generated either through chemical reaction or bacterial action • Chemical reaction occur over time as heat and pressure are applied to coal in sedimentary basin, referred to as thermogenic methane. • Bacteria obtain nutrition from organic matter and produce methane as a by product, is referred to biogenic methane.

• Methane is held in the cleats with the coal • Substantial water pressure is needed to keep the methane in the coal

FORMATION OF METHANE DURING COALIFICATION PROCESS

METHANE STORAGE IN COAL Methane in coal is: • Adsorbed on the surface of the coal • Stored as free gas in the cleats and open pores

STAGES OF DEVELOPMENT (CBM) • Coring

Casing Type

Hole Size

Casing Size

Details

Shoe Depth

• Drilling

Conductor

17 ½”

14”

ERW pipe

~18 m

Surface

10 5/8”

8 5/8”

24 ppf, K55,

200 m

• Casing & Cementation • Cased hole Logging & Perforation • Well Testing • Hydraulic Fracking • Well Completion • Production

CORE ANALYSIS • Gas volume • Gas composition • Coal description • Adsorption isotherm • Proximate analysis • Ultimate analysis • Vitrinite reflectance • Bulk density determination

STC Production

7 7/8”

5 ½”

15.5 ppf, K55, BTC

Set at TD

CBM PRODUCTION TECHNIQUES

METHANE DESORPTION • CBM is produced by removing water pressure that holds the CBM in place. • Methane that was held in place by water pressure.

PROGRESSIVE CAVITY PUMP • PCP is a positive displacement pump, where produced fluid is displaced axially at a constant rate. • PCP’S are comprised of two helicoidal gears, where the rotor is positioned inside the stator. • Combination of rotational movement and geometry of the rotor inside the stator results in the formation of cavities that move axially from pump suction to pump discharge.

Bottom Hole Equipment: • Stator • Rotor • No Turn Tool • Rotor bushing • Necessary X-overs & Gas anchors Surface Equipment: • Flow Tee • Hollow Shaft drive head • Intrinsically safe electric motor/hydraulic motor driven by duel fuel engines • Polished rod • Polished rod clamp

PRODUCTION PROBLEMS & NEED FOR WORKOVER Parameter

• Workover refers to any kind of well intervention involving invasive techniques • It can also be described as the process of performing major maintenance or remedial treatment on a oil or gas well.

Workover type

Low water head in

Downsize The Pump

the Annulus Sand Production High Torque

Sand Cleaning

Increases Gas Influx In

Lower the PID

Tubing

• In all the operations, pump is required to stop and in some of the operations downhole pump is to be retrieved. • Most common workover operations includes Sand cleaning & Flushing, Downsizing the pump, Fishing, etc..,

Causes

Elastomer Swelling Downsizing Rotor (Slim Hole Rotor) Pump Unscrewed

Fishing

Sucker Rod

Fishing

Unscrew Low Torque (Mostly Means Fishing)

Tubing / Sucker

Fishing

Rod Shear

Low Production

NTT Fail

Change NTT – Fishing

Tubing Puncture

Replace Tubing

CONSTRAINTS OF CBM AND THEIR POSSIBLE SOLUTONS • Failure in Attainment of Continuous Dewatering (Due to sand production, scaling, sucker rod unscrew, tubing puncture, high torque etc..,) SOLUTION: Eliminating workover is an impossible target but it can definitely be reduced. I.

if a high percentage of sand is pumped out continuously, it may lead to abrasive wear of the rotor and stator. So running a pump with larger displacement per RPM and lower pump speed reduces velocity of the particles within the pump preventing abrasive wear.

II.

The well must be properly swabbed after acid job till the pH of the fluid is back to its original level to avoid acid attack on the rotor and stator.

III.

Proper space-out is mandatory keeping in mind every small factor to avoid the pump locking up and other torsional stresses.

IV.

To avoid elastomer swell, dry run and burning of the elastomer due to friction, the selection of pump model, elastomer-fluid compatibility check and PID selection must be appropriate so that it does not require frequent changes.

V.

If dry run is the result of high percentages of free gas, lowering the pump setting depth or running a gas anchor will limit the gas entry.

VI. There are some mechanical failures like tubing punctures and sucker rods being worn out, and to reduce this, centralizers should be used for each sucker rod and the pump should be operated at an optimum RPM which will decrease the vibrations.

CONTINUED… • LOW PERMEABILITY- (permeability of CBM is extremely low i.e. below 0.1 mD)

SOLUTION- Hydraulic Fracking •

SAND PRODUCTION

SOLUTION- If the permeability even after the HF job is low, therefore gravel packing cannot be used. The only changes which we can make are: I.

Increasing the total depth of the well i.e. the sump.

II.

Using resin coated proppants or sand wedge so that they bind the near well bore proppants and prevent them from accumulating in the sump, thereby reducing the sand production.

• SCALE FORMATION SOLUTION: Only solution for this constraint is injection of biodegradable scale inhibitors in the formation to reduce frequent acid jobs.

• WATER INFLUX DURING DRILLING SOLUTION: The only remedy for this constraint is to shift from air drilling to mud drilling. • SURFACE WATER DISCHARGE SOLUTION: Before disposal it has to be treated, as it contains Trace metals and organics which are carcinogenic

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