The objective of perforating a well: to establish communication between the wellbore and the formation by making holes through the casing, cement and into formation in such a manner so as not to inhibit the inflow capacity of the reservoir. To optimise perforating efficiency, it is not solely down to the perforating technique but relies extensively on the planning and execution of the well completion which includes selection of the perforated interval, fluid selection, gun selection, applied pressure differential or underbalance, well cleanup, and perforating orientation.
Designed & Presented by Mr ĐỖ QUANG KHÁNH, HCMUT 12/2010 Đỗ Quang Khánh – HoChiMinh City University of Technology Email: dqkhanh@hcmut.edu.vn or doquangkhanh@yahoo.com Introduction The objective of perforating a well: to establish communication between the wellbore and the formation by making holes through the casing, cement and into formation in such a manner so as not to inhibit the inflow capacity of the reservoir To optimise perforating efficiency, it is not solely down to the perforating technique but relies extensively on the planning and execution of the well completion which includes selection of the perforated interval, fluid selection, gun selection, applied pressure differential or underbalance, well clean-up, and perforating orientation Basic Perforating Methods Basic Perforating Methods Conventional casing guns which are run into the well on electric wireline with or without wireline pressure control equipment Through-tubing guns which are run into the well after the tubing has been installed, again via wireline pressure control equipment Tubing-conveyed guns which are run on the bottom of the tubing string and detonated using mechanical, electrical, or pressureactivated firing mechanisms Shaped Charge It creates a very high pressure, but a highly focussed jet that is designed to penetrate the casing, the cement and, as far as possible, into the formation Components of Shaped charge Carrier gun arrangement Explosives The main explosive charge is usually a desensitised RDX (Cyclonite) type of explosive which besides being extremely powerful in terms of the energy released per unit weight of explosive, also reacts very quickly In fact, once the main charge is detonated the process is completed after only 100 - 300 µ seconds This fast reaction time is of importance in that it concentrates the detonation energy of the exploding charge to a very limited target area and also excludes any thermal effects Explosive Group Detonation process of shaped charge The importance of using a conical liner in a shaped charge Detonation process and deformation of the conical line Detonation process of shaped charge ms ms 9.4 ms 16.6 ms Detonation process of shaped charge Perforating jet characteristic and properties at impact with the target Crushed zone and compaction regions around the perforation tunnel Wireline Conveyed Casing guns Retrievable hollow carrier guns: Casing ranges from 1/8 in (7.9 cm) up to in (12.7 cm) A running clearance of 0.5 in (1.3 cm) is a typical rule-of-thumb allowance for trouble-free entry Common design: 4SPF Length limit: 30-40 ft for large diameter guns, and 60-80 ft for small diameter guns Expendable and semi-expendable guns: Casing ranges from 1/8 in (7.9 cm) up to in (10 cm) Length is much longer (up to several hundred of feet) Wireline Conveyed ThroughTubing guns Be run in after the well mechanically complete & the equip pressure tested, the well can be perforated under drawdown Wireline Conveyed ThroughTubing guns Through-tubing guns have smaller diameters than casing guns to allow passage through tubing or small-diameter casing strings Carrier swelling (due to the force of explosion) may be reduced by maintaining a minimum hydrostatic pressure on the gun during firing (0 and 500 psi in liquid and 500 to 4500 psi in gas-filled boreholes) Tubing-Conveyed Perforating guns TCP: o the assembly of a perforating gun on the end of drill pipe string, production tubing or coiled tubing and its lowering and positioning in the wellbore prior to detonation o The technique has increased rapidly in both application and development during the 1970s and is now widely employed o After detonation, the gun can either be pulled from the well or detached to drop into the wellbore sump below the perforated interval Deployment Options o Running the guns with a conventional drill stem test assembly o The gun could be run attached to the base of the completion string tailpipe below the packer The string would be run into the hole, landed off, the packer set and the gun detonated under drawdown Normally, the guns would be detached and dropped into the sump o Running and retrieving the gun on coiled tubing using a CT deployment system Tubing-Conveyed Perforating guns Common configuration for TCP system Tubing-Conveyed Perforating guns Firing Options: When the gun is in position, it can be detonated by: (1) Mechanical firing: A bar or go-devil can be dropped down the tubing onto a plunger which contacts a blasting cap on top of the gun.=> unreliable if debris is allowed to accumulate on top of the firing head (2) Hydromechanical: the annulus can be pressured up and the pressure routed through a bypass valve above the packer, onto a series of shear pins on the firing head Once a differential pressure is exerted sufficient to shear the pins, the firing pin is driven down against the detonator => more reliable than in deviated wellbores (3) Wireline firing: a special wet connect is run on wireline after the guns are positioned -> attaches to the firing head which can then be fired by passing an electrical current down the cable from surface.=> besides surface pressure being created on successful firing, there are also electrical indications at the surface TCP Gun Disposal: o After detonation the gun can be dropped However, if it is decided to flow the well either before detaching the gun, or if it is intended to retrieve the gun, a vent assembly or perforated joint must be provided below the packer where fluid can enter the flow string Tubing-Conveyed Perforating guns Advantages: o Combines large gun size with high negative pressure differential o Allows easier perforation of long pay intervals o Allows easier perforation of highly deviated wells Disadvantages: o Impossible to confirm individual charge detonation o Needs significant rat-hole to receive guns after firing, unless guns are to be retrieved o Added expense, particularly when perforating a few small zones over a large interval API Testing Procedures Section 1: The surface field test is carried out in a section of casing cemented inside a concrete drum Section 2: The laboratory flow test is carried out using a Berea sandstone target that is cemented inside a core holder designed to permit flow through the perforation Section 3:The elevated temperature and pressure test involves (a) firing a gun into a steel target after exposing the gun to rated temperature conditions for a specified time period; (b) testing the resistance of gun components to automatic self-detonation; (c) confirming satisfactory detonation transfer between guns; (d) testing the pressure resistance of gun components Section 4:The flow test is an optional test that measures perforation flow performance on a Berea core or other rock sample, under simulated, site-specific downhole conditions Section Testing Measured values: casing hole diameter (short axis, long axis, average) total penetration burr height depth to debris or bullet Section Testing Courtesy of Schlumberger Section Testing Performance in stressed Berea sandstone targets (simulated wellbore pressure test conditions) Effect of overburden or confining stress to be evaluated The data from this test can be extrapolated to penetration in any reservoir of knowncompressive strength using: Ct = Compressive strength of test material, psi Cf = Formation rock compressive strength, psi Pt = Penertration measured in API test, inches Pf = Penetration predicted for formation rock, inches The core flow efficiency (CFE): ko = original target permeability measured prior to perforating (saturated with salt water and then flowed with kerosene, generally 100 to 300 md for Berea) kp = perforation permeability measured after perforating and backflow using kerosene ki = effective permeability of a Berea sample with an "ideal" (drilled) perforation of the same length as that in the perforated target Section Testing Temperature/Time test of explosive components Obtain hole size, penetration in steel targets and compare them with performance at ambient conditions Evaluate system’s liability at rated pressure/temperature Seal failure, hardware deformation, and collapse at 1.05 times the rated pressure Section Testing Flow performance of a perforation under specific stressed test condition Flow test of a confined rock target Single shot Data obtained: Core Flow Efficiency (CFE) Permeability Reduction Factor (PRF) Perforating Gun Design (courtesy of Schlumberger) Operational Considersations Surface Pressure Equiptment Depth Correlation Safety Procedures Gun Length/Perforated Interval Perforating Multiple Zones Temperature Effects Casing Damage Gun Orientation Charge Quality ... applied pressure differential or underbalance, well clean-up, and perforating orientation Basic Perforating Methods Basic Perforating Methods Conventional casing guns which are run into the well... so as not to inhibit the inflow capacity of the reservoir To optimise perforating efficiency, it is not solely down to the perforating technique but relies extensively on the planning and execution... psi in liquid and 500 to 4500 psi in gas-filled boreholes) Tubing-Conveyed Perforating guns TCP: o the assembly of a perforating gun on the end of drill pipe string, production tubing or coiled