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Perforating > FAQsCHARGE FAQsCARRIER FAQs GENERAL PERFORATING FAQs Charge FAQsIf you have a question, simply ask it via our contact us form.What is flow area, how is it calculated and how does it relate to productivity in a well? What is salt and pepper perforating? What makes a big hole charge big and a deep penetrating charge deep? How is a shaped charge named? How does the exit hole on a carrier relate to that of the perforated casing? Who is our main shaped charge supplier and how often do we get shipments from them? Do you think it is a good idea to have all the different charge suppliers and do you stand behind all the different products? How do you define a debris free charge? What does it mean when charge data is normalized? What is charge interference and how does it affect performance? What is API data and how does it relate to QC data? What is the difference between RDX and HMX performance? What is flow area, how is it calculated and how does it relate to productivity in a well? The flow area of the perforations is the sum total of the area created by the shaped charges in the casing during perforating operations. This number is usually presented in terms of square inches per foot per or square centimeters per meter of carrier. The formula for calculating the flow area is F = .785 x (D)2 x SD D = diameter of entrance hole (EH) SD = shot density (SPM or SPF) For example a well is perforated at 8 SPF using a big hole shaped charge with an EH of 1.02". Using the above calculation the flow area would be 6.53 sq. in./ft. Using Metric measurements it would be 134.15 sq. cm./m Why is flow area important to perforating and productivity? In simple terms the larger the perforations in the casing and the greater the number of perforations, the better the hydrocarbon flow becomes and the better the wells productivity. In many areas of western Canada when perforating in unconsolidated sand formations (especially in the regions of heavy oil development) well operations have noted a significant drop in production due to sand migration into the perforations. This phenomenon occurs as a pressure gradient is formed across the perforations during the production phase of the well which carriers sand with it. This effect is most pronounced when the well is perforated with Deep Penetrating (DP) style of shaped charges. To counter this well operators have gone to using larger perforation tunnels created by a Big Hole (BH) shaped charge. The larger the hole in the casing the less of a pressure gradient is created. This is similar to the effect of blowing across the top a glass pop bottle. The narrower the neck (like a DP) the higher the pitch created and vice versa. 
What is salt and pepper perforating? Salt and pepper perforating is the practice of alternating deep penetrating charges and big hole charges in the same carrier. While the shaped charge manufacturers like Titan Completions, GOEX or JRC have never tested this system, it has been used with varying degree of success in regions of heavy oil production. Normally the operator would have the carriers loaded with charges of compatible gram weight i.e. 32gm charges alternating big hole and deep penetrator. The theory behind using charges of different style in the same carrier is that during the drilling process the formation can be eroded or washed out. When this occurs in the zone of interest and the production string is cemented in place it may be impossible for a big hole charge to completely penetrate the cement surrounding the pipe. This would prevent communication from the pay zone of the formation to the well bore. To lessen this possibility deep penetrating charges are used to increase the depth of penetration and allow for some production to occur. Under the right conditions the combination of DP and BH charges can be effective.
What makes a big hole charge big and a deep penetrating charge deep? In terms of specifications a shaped charge is classified as a big hole when it creates an entrance hole (EH) in excess of 0.55" and a super big hole (SBH) is any shaped charge that creates a EH in excess of 0.80". The deep penetrating charge category consists of any charge that creates a deep perforation tunnel. This value is charge specific. What makes a big hole charge a big hole charge and not a deep penetrator is in the science of the liner and its design. In general a big hole liner is shaped like a shallow dish and a deep penetrator is more like a cone. This change in shape allows for a variation in focus point of the jet stream when the charged is detonated. The shallow focus point of the big hole allows for a broader, fuller jet stream to develop which in turn creates a big hole in the casing and into the formation. However this larger jet stream tends to loose energy rapidly. Therefore it may not penetrate the formation beyond ~12". A big hole charge is mainly used in regions of heavier API gravity oil production. The Lloydminster area is an example of this type of production. The bigger entrance hole permits a greater flow area. The opposite is true for the deep penetrating charge. Its longer focus point due to the conical nature of the liner creates a smaller EH but tends to penetrate the formation to a greater degree. Depending on charge gm. weight and the composition of the liner material this can be upwards of 45". You normally see deep penetrating charges used in tightly compacted sands or carbonates.
How is a shaped charge named? Each manufacturer has their own unique way of naming charges according to their own manufacturing criteria. For example Titan Completions has a chart that encompasses a number of charge attributes including type & style of charge, gram weight, carrier size, powder temp rating and so on.
How does the exit hole on a carrier relate to that of the perforated casing? It has often been observed that exit hole on a spent carrier while round or nearly round is not as large as the published data suggests. The reason we see this is because of clearance. Which is the distance from the edge of the scallop to the inside edge of the casing being perforated. Charge manufactures perform static QC tests on surface using known carrier parameters including clearance, fluids, carrier wall thickness and scallop depths. This data approximates everything that the shaped charge will encounter in a real well situation and is recorded as QC or quality control data. In the above case we see what the charge saw as it exited the carrier and not what the casing experienced. Depending on what type of shaped charge you are dealing with the jet stream may still be developing as it exits the carrier and before it reaches the casing a nanosecond later.
Who is our main shaped charge supplier and how often do we get shipments? Explosives Limited has distribution agreements with all major manufacturers of shaped charges. Titan Completions of Mansfield Texas are currently providing about 70% of our products for distribution. We normally receive a weekly shipment of shaped charges from Titan and our other suppliers.
Do you think it is a good idea to have all the different charge suppliers and do you stand behind all the different products? The ability to provide shaped charges from all of the major manufacturers allows us the flexibility and freedom of choice both in product and delivery for our customers. Explosives Limited always stand behind those products as well as any other that we service or sell.
How do you define a debris free charge? ‘Debris free’ refers to the amount of residual material remaining after detonation of a big hole charge. We classify debris free charges in three ways: 1) By liner composition. A debris free liner material would leave little if any carrot (slug) in the perforation tunnel. 2) The charge case material composition is normally a zinc-based material in a debris free charge. This material breaks down into a powder-like substance after detonation. 3) A true debris free charge would combine points 1 & 2 (above) and leave very little ‘junk’ in the well after perforation.
What does it mean when charge data is normalized? All manufacturers furnish charge performance data from the results of QC or API tests. Testing is done by shooting shaped charges into concrete targets with a compression strength specific to the target. It has long been known that the compression strength of the concrete directly effects the TTP value of the charge. Normalization. is a mathematical attempt to present an ‘apples to apples’ comparison using equivalent concrete strengths. Industry standards use a 3.8% increase (as referenced by SPE paper #27424) in penetration per 1000 psi above 5000 psi concrete. For example: a test charge yields a value of 28.5" in 6000 psi concrete target. To normalize this charge to a 5000 psi concrete target you would use the following calculation... TTPN = TTP + (TTPx3.8%) x (TPSI-5000)/1000. Where TTPN would be the normalized value in inches. TTP would be the original through target penetration value. TPSI would be the compression strength of the target material.
What is charge interference and how does it affect performance? Charge interference occurs when the blast effect from one charge deflects or bends the jet stream from its meighbouring charge. Effect is more pronounced at higher shot density. In a bottom fired gun, the jet stream will bend upwards with increasing intensity. This will therefore cause the effective perforating tunnel to shorten and become less efficient. To help alleviate this problem, XHV detcord should be used on all carriers shot at 17 SPM or greater.
What is API data and how does it relate to QC data? API (American Petroleum Institute) has initiated a standard set of criteria to test perforating systems for the presence of charge interference. This test data must be recorded and reflect the test parameters. QC data is recorded in order to insure charge performance falls within usual or acceptable statistical variations. On any particular charge it can range from one in 25 to one in 500 depending on the manufacturer and its policies.
What is the difference between RDX and HMX Performance? We have received numerous questions concerning RDX versus HMX charge performance. To answer this, Titan Completion have made an industrywide examination of API performance data and found that there is no significant difference. Click here to download a PDF file on this topic.
Carrier FAQsIf you have a question, simply ask it via our contact us form.Where are perforating carriers made and what kind of steel is used? Why do we need to shoot wells dry or with fluids present? How much fluid above the gun is enough to safely perforate? What is gun jump? Why do we employ phased carriers in perforating operations? What phasing patterns are available? Sometimes carriers get stuck in the well after perforating. Why does this happen? What gun systems will you be stocking for all the different charges that you maintain in stock? How is performance effected when a shaped charge misses the scallop? Where are perforating carriers made and what kind of steel is used? At Explosives Limited most of our expendable carriers are made for us by our sister company, Natayo Manufacturing located in Calgary. We also import some of our products from Titan Specialties in Pampa, Texas. Explosives Limited carriers are created using steel from a limited number of quality manufactures. For the majority of our expendable carriers we use material supplied to us from Bentler Steel in Germany. This high grade, uniform product is recognized worldwide as the best available. Other steel suppliers include US Steel and Lonestar steel both from the United States.
Why do we need to shoot wells dry or with fluids present? The completion technique required to successfully perforate a well is dependent on a great number of factors. These could include depth of well, presence of sour fluids (those containing H2S), perceived formation pressures, formation susceptibility to fluid invasion, type and thickness of reservoir rock etc. Generally speaking we see the use of dry shooting (i.e. perforating with little or no fluids in the well bore) mostly accomplished in Southern Alberta. In that region perforating activities are centered on development of shallow gas reserves. These formations such as the Milk River are usually thin clean sand stringers in the order of 2–3 meters thick that are prone to formation damage when perforated under fluid conditions. By perforating dry they run less risk of damaging the formation. However there is an increased risk to the cable (wireline jump) and to the carrier. In fluid filled perforating a fluid column is present above the carrier. This column of borehole liquids acts as a safety barrier for any unknown (or known) formation parameters. For example; a highly pressured gas zone with some H2S content. Fluid filled perforating is still the preferred method of completing wells in western Canada and around the world.
How much fluid above the gun is enough to safely perforate? Normally a perforating company would like to see as much fluid above the gun as possible. However reality and practicality suggest that at least 50 meters is acceptable when perforating under fluid conditions.
What is gun jump? Gun jump can occur through a couple of processes. It is mainly created when a well is perforated dry at or near the bottom of a well. It is here that the escaping perforating gun gasses act upon the bottom surface of the carrier and force it upwards. When this happens it usually creates a ‘birds nest’ in the wireline due to a lack of tension in the cable. This can result in damage to the line. A second occurrence of gun jump can happen as a consequence of formation surge. In this case a strong rush of gas flowing from the formation as a result of the perforating helps push the carrier upward and damage the line. Tools known as perforating gun brakes have been developed to help combat these negative effects.
Why do we employ phased carriers in perforating operations? What phasing patterns are available? We use phased carriers for a number of reasons. Most commonly we use phased carriers as a method of increasing the shot density. That is the number of available shots in a given interval length of expendable carrier, ported carrier, ECO II or other style of perforating system. This value is seen as shots per meter (SPM) or shots per foot (SPF). Shot densities can range from 1 to 118 SPM depending on the system. Phase patterns likewise are diverse in nature. Patterns range from 1 shot every 10 deg. around the carrier to 1 shot every 0/360 deg.The latter is known as 0 (zero) degree phasing. Phasing may also be limited by the style of carrier used for perforating. In some applications such as through tubing perforating the carrier may be limited to zero degree or 180 degree phasing.
Sometimes carriers get stuck in the well after perforating. Why does this happen? From time to time carriers do get stuck in the well after perforation. This can occur for a number of complex or not reasons. Look at the problem in its simplest terms. A carrier is designed to perforate with a certain size casing in mind. For example a 4" carrier is designed to run safely in a well with 5 1/2" production casing. Gun manufacturers take into account a number of factors such as density, gram weight, wall thickness, fluids or not etc. From that data and surface tests they deem a carrier safe to run under those conditions. Here’s where the fun begins. The carrier is detonated and all goes well until the carrier is brought to surface. It jambs in the casing and despite the best efforts of the crew they can not retrieve it and end up pulling out of the rope socket and weak point. After successfully fishing the carrier out of the well it was discovered that 5 charges near the bottom fired but did not produce clean even exit holes. Upon further investigation it was determined that the bottom charges fired under what is called low order due to being wetted out. Fluid was inside of the carrier. This happens rarely and is usually caused by a failure of the lower o-ring. The above situation illustrates one possibility as to how a carrier can become stuck in a well. Mother Nature and human nature both suggest that failures will and do occur in the world of perforating.
What gun systems will you be stocking for all the different charges that you maintain in stock? Currently we are providing a comprehensive stock of perforating carriers for our customers. These range in sizes from 1 9/16" to 5" O.D. and in lengths from 0.3 meter to 6.0 meters. We also provide by special order length upto 9 meters. Natayo Manufacturing and Titan Specialties manufacture the majority of our carriers. Some of our specialty carriers (i.e. through tubing applications) come to us via other suppliers.
How is performance effected when a shaped charge misses the scallop? Our research suggests that charge performance is downgraded by 3-5% when a charge misses the scallop. For example: a deep penertrating charge shooting 25" through the scallop will loose 0.75" to 1.25" of penetration with minimal change in entrance hole. Big hole charges exhibit exaggerated alteration under these conditions. Our testing of big hole charges shot in scalloped carriers versus non-scalloped carriers showed a penetration downgrade of upto 50% and dramatic decrease in entrance hole. Please contact us if you would like a copy of the big hole test results!
General Perforating FAQsIf you have a question, simply ask it via our contact us form.What is TCP and when is it used? Does temperature affect charge performance? How fast does a perforating system work? What components comprise a conventional perforating system? What are the conversions for shot densities from shots per foot to shots per meter? What are the conversions from Imperial to Metric measurements for the common carrier & production casing O.D.'s? Do you offer training? What is TCP and when is it used? Tubing Conveyed Perforating is also known as TCP. It is a method of lowering and positioning perforating carriers in a well and detonating from surface using a mechanical style of detonation system. This type of perforating is used when wells formation conditions or orientation demands that absolute well control is maintained. In some cases the well may need to be perforated when it is in an under balanced condition. This means that the pressure from the weight of the fluid column is less than that expected in the formation. Upon perforation no fluids from the well bore will invade into the formation and possibly damaging the hydrocarbon zone. Conversely a well may be perforated in an overbalanced state. Here a well is purposely flood upon perforating to create a flushed zone. Lastly when a well is severely deviated it may not permit conventional perforating tools to be lowered into position. This would limit the usage potential of those tools.
TCP is accomplished by use of mechanical detonation as opposed to electrical detonation for conventional perforating systems. By using a variety of firing systems such as; Direct Pressure Vent, Pressure Activated, Mechanical Bar Drop and Time Delay, the carriers and shaped charges can be activated with no direct link to surface equipment. Does temperature affect charge performance? If so what changes need to be done to correct those effects. Temperature does have an impact on performance of a shaped charge. All charges are rated over time at a specified temperature (normally at some value for 1 hour). A charge that uses RDX powder will begin to gas off or breakdown after the recommended values have been exceeded. When this occurs the charge performance will drop significantly or not detonate at all. The remedy is to employ a charge that uses HMX as its main powder. The composition of this style explosive allows it to withstand greater temperatures for longer periods of time.
How fast does a perforating system work? The speed at which a perforating system works is related to the sum of its components. Generally a system detonates at approximately 25,000 ft/sec. The charge jet stream instantaneously exerts pressures of upto 6 million psi at temperatures of 6000 deg F. At those values the complete detonation of the carrier takes only fractions of seconds.
What components comprise a conventional perforating system? A perforating system consists of 8 main components. These include; 1) Firing Head. Is the connection point from the wireline or cable to the perforating carrier. If something should happen to the carrier and it not possible to remove it from the well a built in weak point is located within the head assembly. This facilitates cable removal from the well without extensive damage. 2) Blasting wire. In conventional perforating an electrical connection must be maintained from the surface in order to fire the detonator. The blasting wire connects the detonator to the firing head. 3) Detonator and Boosters. The detonator accepts the current from the blasting wire and fires a resistor. This action energizes the small lead azide pellet in the detonator and ignites the primacord boosters carry the detonation front from one carrier to another in tandemed gun systems. 4) Primacord. Carries the detonation front along the path to the back of the shaped charges. This detonation front moves along at ~25,000 ft./sec. The primacord needs to have intimate contact with the back of each charge to insure proper detonation occurs. 5) Shaped charges. They are the one component in the perforating system that actually does the work on the casing to create the desired effect. Depending on style and gram weight the perforations can range to over 1". 6) Load tube. This component holds the shaped charges securely in place, in the correct phasing and charge density. 7) Perforating carrier. This is where the charges secured by the loading tube are held during perforating operations. The carrier is isolated from well bore fluids by use of o-rings and subs. 8) Bottom Sub. Often called the bull nose. This component is usually a threaded solid metal part that can withstand the considerable internal force of gun gasses produced during the perforating operation.
• What are the conversions for shot densities from shots per foot to shots per meter? The conversions are as follows:
What are the conversions from Imperial to Metric measurements for the common carrier & production casing O.D.’s? The conversions are as follows:
Do you offer training? Yes, and you can find out more on our training page.
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