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Bullet gun, abrasive, water jets, and shaped charges are perforating methods used to initiate a hole from the wellbore through the casing and any cement sheath into the producing zone. Bullet speed exiting the barrel is usually approximately 900 m/s (3000 ft/sec). Penetration is easiest in low alloy, thinner walled pipe [H-40, to K-55, and L-80 American Petroleum Institute (API) casing series pipe grades]. Penetration in higher strength casing alloy pipe and harder formations is more difficult in most cases and not feasible in others. When successful, the bullet creates a very round entrance hole but may often create a hole with sharp internal burrs.
Conventional well completions in soft formations (the compressive strength is less than 1,000 psi) commonly produce formation sand or fines with fluids. These formations are usually geologically young (Tertiary age) and shallow, and they have little or no natural cementation. Sand production is unwanted because it can plug wells, erode equipment, and reduce well productivity. It also has no economic value. Nonetheless, formation sand production from wells is dealt with daily on a global basis.
Prepacking can be defined as any method that intentionally places gravel into the perforation tunnels. Filling of perforation tunnels can be accomplished either with a dedicated operation before performing the gravel pack or simultaneously with it. The technique used is normally dictated by well parameters. Gravel packing cased-hole completions in vertical and deviated wells are more common than openhole completions, particularly in shaley reservoirs. However, cased-hole gravel packs have an important requirement that is easily overlooked.
Because many of the perforating processes deal with explosive powders and gas expansion methods, a few definitions of the specialized nomenclature are needed. High explosives are very powerful explosives such as RDX, HMX, PYX, HNS, and others that find common use in the oil industry. High explosives are characterized by extreme energy release in a very short time, some with detonation front movement on the order of 6100 m/s (20,000 ft/sec). The detonation of an explosive is a chemical reaction and, like many chemical reactions, certain variables control the speed of the reaction. Peak energy generation with these materials is necessary to perform effectively and can be achieved only if they have high-order initiation. The initiation process for any explosive is critical in oilfield applications. Gas generators are explosive materials designed to generate energy at a slower rate than the high explosives, and their primary function is to provide quick fluid volume. These materials are used for power fluids (gas drive), fracturing energy, and propulsion energy sources. Order is a term associated with explosive firing. High order means that the high explosive has been initiated properly and reacts at the maximum speed. Low-order initiation of a high explosive fails to achieve maximum energy; the explosive may react, but the energy level produced is sharply lower than the maximum potential.
Formation damage caused by drilling-fluid invasion, production, or injection can lead to positive skin factors and affect fluid flow by reducing permeability. When mud filtrate invades the formation surrounding a borehole, it will generally remain in the formation even after the well is cased and perforated. This mud filtrate in the formation reduces the effective permeability to hydrocarbons near the wellbore. It may also cause clays in the formation to swell, reducing the absolute permeability of the formation. In addition, solid particles from the mud may enter the formation and reduce permeability at the formation face.
A new perforating technique employing the integration of conventional shaped charges and solid propellant was described by Albert, et.al. (SPE 197185-MS). The innovative propellant deployment method allows the propellant deflagration to occur in the perforation tunnel rather than gun body and casing, thus delivering maximum energy to improve perforation tunnel performance. Shaped charges utilizing high energy explosives perforate casing and formation with high speed metallic jets that displace by sheer force. The explosive events are fast (20-30 microseconds) high impact events (as high as 1.5 million psi at the rock face) that can collapse large pores in the formation along the surface of the perforation tunnel. This crushing along the tunnel reduces permeability and increases skin and can impact the flow of fluids into and out of the reservoir rock. A number of methods have been developed to improve perforation tunnel flow efficiency, but all suffered limits on either deployment or effectiveness.
Propellants have been used for decades to improve perforation performance. Propellants are energetic materials with slower burn rates that can micro-fracture the formation and break-up the crushed zone around perforation tunnels. Prior methods deflagrated the propellant materials within the gun bodies, or casing and lost a significant amount of energy before delivering impact to the perforation tunnel. The new method with a composite cap of solid propellant on the face of the shaped charge, displaces the propellant into the perforation tunnel before deflagration, thus delivering maximum energy to the formation. This helps break up the crushed zone and micro-fracture the formation.
The improved perforation tunnel will reduce frac fluid tortuosity. Frac jobs can get better fracture initiation and better proppant placement, resulting in better production. This paper will focus on additional lab testing at an Advanced Perforating Flow Laboratory plus several USA onshore completions (horizontal and vertical). The field data will show the effect of the composite perforation method on frac performance and well production.
Perforations are used to flow hydrocarbons into a well. Impeding that flow are damaged zones from drilling and the crushed zone lining the walls of perforation tunnels into the rock. In addition, charges can affect a region beyond the crushed zone. This region is termed the "fracture damage zone," and the nature of this region is examined in this paper. The fracture damage zone is the area where the concrete model shows altered effects. This region of damage is not necessarily failed, but is the most likely region of fracture. This work discusses the use of a shock hydrocode to delineate this region. Because the hydrocode is a continuous code, specific fracture paths are not predicted. The code is run for big hole (BH). deep penetration (DP), and fracture (Frac) shaped charges. The damaged region is compared for the types of shaped charges. Simulation results indicate that the region of fracture damage follows the bow shock. This semicircular bow shock region continues propagation after the jet has stopped, but eventually diminishes outward from the jet origin. Generally, the BH charge has a wider damage region than the DP charge, with the DP charge damage region being narrower and deeper than the BH (because of the depth of penetration). The damage zone of the Frac charge is between those of the BH and DP charges. In addition, the damaged region may not be sufficiently affected to actually create failure caused by fractures. "Distance" to the fracture limit is characterized. This ready-to-fracture region is discussed in terms of making it a failed fracture region by external influences, such as propellant stimulation.
Petroleum wells producing water are likely to develop deposits of inorganic scales that may form near the wellbore and may plug perforations, coat casing, production tubulars, valves, deteriorate pump performance, and affect downhole completion equipment. Scales form and precipitate because the solution equilibrium of water is disturbed by pressure and temperature changes, dissolved gases or incompatibility between mixing waters. If scale formation and precipitation are allowed to proceed, scaling will limit production, eventually requiring abandonment of the well. In order to remove the effects of scale on production after a well undergoes sharp or early decline in production, it is essential to first determine which scales are forming and where they are forming. Some of this information can be reliably inferred from computer simulation procedures or by running calipers down the wellbore and measure decreases in the tubing inner diameter so that the scale can be physically detected. Gamma ray log interpretation may also be used to detect barium sulfate scale because naturally radioactive radium precipitates as an insoluble sulfate with this scale. Scale remediation techniques must be quick and nondamaging to the wellbore, tubing, and the reservoir. If the scale is in the wellbore, it can be removed mechanically or dissolved chemically. Selecting the best scale-removal technique for a particular well depends on knowing the type and quantity of scale, its physical composition, and its texture. Mechanical methods such as Dynamic Underbalance Pressure (DUP) technique are among the promising methods of scale removal in tubulars and across perforations. The purpose of this work is to present a case study of removing barium sulfate (BaSO4) scales from perforation tunnels utilizing dynamic underbalance technique. Wells from a North African oil field were selected for designed and optimized dynamic underbalance treatments to remove barium sulfate scales that precipitated in the perforation tunnels, preventing hydrocarbons flow from the formation to the production tubing. Gamma ray log and production logging tool were used before the treatment to detect and evaluate the type of scale and the intervals affected. Then the same tools were used after the treatment to assess stimulation taking place in the wells. Data obtained from the treatment was used to develop a model for predicting productivity index/inflow performance relationships. The dynamic underbalance technique successfully removed scale from all targeted wells, leading to an increase in oil production, without killing them (i.e. while still in production). Some wells achieved increase in oil production after the treatment of up to 65%. A predictive model was developed in order to estimate the performance of an underbalance scale removal treatment.
Mohamed Elkordy, Mohamed (Kuwait Oil Company) | Taqi Akbar, Bader (Kuwait Oil Company) | Kumar Patra, Milan (Kuwait Oil Company) | Ahmad, AbdulSamad (Kuwait Oil Company) | Abu Eida, Abdullah (Kuwait Oil Company) | Al Azmi, Nasser (Kuwait Oil Company) | Dashti, AbdulAziz (Kuwait Oil Company) | Abouganem Stephens, Alberto (Schlumberger) | Ayyad, Hazim (Schlumberger) | Abdulrahim, Khaled (Schlumberger) | Al Busaidy, Adil (Schlumberger) | Luna Hernandez, Guillermo (Schlumberger) | Grabssi, Wahiba (Kuwait Oil Company)
To reactivate wells that are not flowing, a common solution is to perforate any bypassed zone to bring the wells back to operation. If the completion does not allow for optimal interventions, i.e. running the perforating gun sized for the target interval, the consequences of a thru-tubing intervention must be evaluated based on cost, probability of success, risk and whether the potential results and the time savings of a rig are justifiable.
In a well in Minagish Field of Kuwait, a combination of thru-tubing technologies was deployed for perforating a bypassed zone, reducing the cost of a rig workover, and maximizing the potential results. The conveyance method was selected in consideration of well access, cost, provision of positive depth correlation, and the capability to deploy the perforating guns thru tubing. Second, the perforating system was modeled with the reservoir parameters for its impact on well productivity. After the perforation parameters were obtained, the application of post-perforating dynamic underbalance was proposed to clean the perforations and reduce skin. Downhole measurements while perforating was combined with all the runs, including gamma ray, collar locator, pressure, temperature. A fast gauge was run in memory mode with the post perforating underbalance guns.
The perforating operation was performed with a suite of measurements conveyed with digital slickline, enabling a cost-effective, informed intervention that reduced the operator’s cost by USD 288,000 over a conventional rig-based operation. The combination of extra-deep penetrating shaped charges loaded a 2-1/8-in phased exposed carrier perforating guns system and the post-perforating cleanup system, restoring the well to a production of 1,500bbl/d.
The application of digital slickline that provided downhole measurement while perforating was deployed for the first time in Kuwait. The use of productivity modeling for perforating proved to be a successful metric for decision making when selecting this intervention methodology. This approach saved the operator time and cost while cutting risks and maximizing the potential production restoration.
This paper presents a field study of reperforation on three vertical oil producers wells suffering poor reservoir quality by combining deep penetration charges guns with propellent materials. Perforation charges will form the perforation tunnel and secondly the burning of the propellent material will create high gas pulse that will go through the perforating tunnels and create near wellbore fractures to overcome the near wellbore damage and improve communication with the reservoir and hence improve productivity.
Propellent simulations were carried out and results show the ability to create fractures and the estimated fracture lengths would extend beyond the wellbore damage, improving the communication between the formation and the wellbore. The propellent is in the form of sleeves installed and secured over the conventional gun carrier loaded with deep penetration charges. When the guns are detonated, the sleeve charge is ignited and instantly producing a burst of high-pressure gas which goes through perforating tunnels to generate fractures near the wellbore. The perforating job was designed with the wells on balance to enhance their productivity. The guns with propellent sleeve were successfully deployed in the wells with downhole pressure transient recorded using fast-recording pressure gauge.
After this work on Well-1, Well-2 and Well-3, several months of production monitoring of those wells show the success of the technique and demonstrate an area of applicability in such mature, low pressure reservoir suffering from near wellbore damage. The simulation of the work and how the actual gauge job data matched the simulation have been an important factor in the success in enhancing the well real performance.