SPE/IADC Introduction

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1 SPE/IADC Application of Laser Technology for Oil and Gas Wells Perforation Mahdi Bakhtbidar, Mohsen Ghorbankhani, SPE, Young Researchers Club, Omidieh Branch, Islamic Azad University, Omidieh, Iran, Mohammad Reza Kazemi Asfeh, Mehdi Alimohammadi, SPE, Department of Petroleum, Omidieh Branch, Islamic Azad University, Omidieh, Iran, Pegah Rezaei, Department of Nature source, IAUA Copyright 2011, SPE/IADC Middle East Drilling Technology Conference and Exhibition This paper was prepared for presentation at the SPE/IADC Middle East Drilling Technology Conference and Exhibition held in Muscat, Oman, October This paper was selected for presentation by an SPE/IADC program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been reviewed by the Society of Petroleum Engineers or the International Association of Drilling Contractors and are subject to correction by the author(s). The material does not necessarily reflect any position of the Society of Petroleum Engineers or the International Association of Drilling Contractors, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Society of Petroleum Engineers or the International Association of Drilling Contractors is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of SPE/IADC copyright. Abstract In gas and oil well completion, perforation channels must be made through the steel casing wall and cement and into the rock formation in the production zone to allow formation fluid to enter the well. This paper will present study results on using a pulsed CO 2 laser to drill the perforation channels through reservoir rocks. With fiber optic cable delivery capability, a CO 2 laser beam has the potential to be delivered to deep oil production zones. Effects of laser pulse parameters, beam properties, and assistant gas purging on the perforating efficiency and rock permeability will be reported. Unlike the conventional explosive charge perforation that often causes great reduction of rock permeability, laser perforation would enhance the rock permeability, therefore increasing the oil or gas production rate of the well. Laser on time, laser relaxation time between laser bursts and sample rotary speed also affect the perforation. A laser burst is the sum of the multiple pulses over the period of laser on time. Pulsed CO 2 laser with fiber optic cable delivery is a strong candidate for laser perforation application for oil and natural gas wells. Preliminary test shows that CO 2 laser can perforate the rock as efficiently as the other types of high power lasers and the permeability of the rock lased by pulsed CO 2 laser beam increases up to 566% compared to non-lased rocks due to clay dehydration and microfractures induced by the high temperature gradient and phase transformation volume expansion generated in the rock while lasing. Introduction Perforation There are different methods that can be used to create perforations in wellbores. One of the first was bullet perforating which was conceived and patented in The major drawbacks with this method were that the bullet remained in the perforation tunnel, penetration was not very good, and some casings could not be perforated effectively. In January 1945, Ramsey C. Armstrong founded Well Explosives Company, Inc. later to be known as WELEX. In 1946, Welex introduced the shaped charge. The principle of the shaped charge was developed during World War II for armor piercing shells used in bazookas to destroy tanks. This new technology allowed the oil producers to have some control over the perforating design (penetration and entry hole size) to optimize productivity. In 1949, McCullough Perforating Company made an attempt at developing tubing conveyed perforating but was not successful. In 1970, Vann Tool Co., known as VannSystems, developed and ran the first commercially successful tubing conveyed perforating system. Throughout the early years, VannSystems was the leader in introducing TCP technology in the oil industry. In October 1985, Halliburton purchased

2 2 SPE/IADC VannSystems and since then Halliburton has continued to be the industry leader in research, development, and introduction of new technology to the oil industry. Figure 1, shows perforation job efficiency since The effectiveness of the communication path through the cement and casing is critical to the completion and well performance. Perforations should enhance well productivity in several ways. They should create clear channels through the portion of the formation damaged during the drilling process. Figure 2, shows schematic of perforated wellbore geometry. They should provide uniform tunnels for hydraulic fracturing fluids and proppants and should make many large uniform holes for sand control and hydrocarbon production. Completions can be classified into four types: openhole, natural, stimulated, and sand control. However, in every case, the objective is to maximize production which, in turn, can be modeled using the radial flow equation (Figure 3): The productivity index (PI), typically used to assess the performance of a well over time, is derived from the following radial flow equation: Skin Factor The skin factor or S term is usually defined as a zone of reduced (or higher) formation permeability near the wellbore. Drilling and completing a well normally results in reduced formation permeability around the wellbore. These decreases in permeability can be caused by the invasion of drilling fluid into the formation, the dispersion of clay, and the presence of mudcake or cement. A similar effect can be produced by reductions in the area of flow exposed to the wellbore. Partial well penetration, limited perforating, or plugging of perforations would also result in a damaged formation response. The skin factor can be used as a relative index to determine the efficiency of drilling and completion practices. The factor is positive for a damaged well, negative for a stimulated well, and zero for an unchanged well. The total skin factor summarizes the change in radial flow geometry near the wellbore due to flow convergence, wellbore damage, perforations, partial penetration, and well deviation. Laser research history Nowadays the issue of modern drilling and finding replacement drilling method for traditional rotary drilling method has received great attention by policy makers in oil industry and drilling engineers. Several replacement drilling methods are recommended for rotating drilling such as: drilling with water vapor, drilling with water pressure and drilling with laser. Among these recommended methods, laser drilling method which has gone under great research and is confirmed by most scholars. Several tests have proved that by using laser drilling technology, it is possible to increase rate of drilling, time of drilling and environmental pollutions. In the present article it is attempted to find suitable relationship between laser technology and drilling industry of oil and gas wells in order to prepare grounds for entering into this industry. Since year 1997, great researches have been conducted in the field of using laser technology in drilling oil and gas wells. The first tests were performed by U.S. army under project called MIRACL. This test indicated that rate of drilling by using laser is increased up to 10 to 100times. Next test was performed by U.S. air force under project called COIL [1]. Several tests were performed in which goal of them was same i.e. laser is able to perform highest level of drilling with minimum required power. On this basis several tests with different parameters were performed including: MIRACL which was performed by Graves and O Brien in which it was used from laser system of continuous waves (CW)

3 SPE/IADC with wavelength of 3.8µm and laser ability of 600KW to 1200KW. In this test during 4.5sec radiation of laser, depth of drilling was reported as 2.5inch for Sandstone. This issue is different for different parameters. Effective parameters on laser drilling are as follows: Power of laser, wavelength, system working mechanism (continuous waves or pulse waves), type of laser and profile of radiation ray [2]. By selecting suitable laser system in accordance with laser parameters it is possible to considerably increase rate of drilling. Until now many advantages have been reported in relation to using laser in drilling oil and gas well including: having ceramic cover on well wall due to melting stone, decreasing working days of drilling rig, decreasing time of stop drilling, having same diameter from surface to bottom of well, decreasing possibility of blocking drilling pipes, considerable decrease in drilling costs, using light weight pipes and replacement of some heavy pipes with fiber optic, decreasing environmental pollution, suitable management of environment and increasing rate of drilling to 10 to 100 times of present value[3]. Replacing rotating drilling with laser drilling had some critics, due to some problems raised during laser drilling which may not be waived including: 1) Rotating drilling fluid during drilling operation and its effect on transferred energy to surface of rocks 2) Transferring energy from laser resource to surface of lens of laser at bottom of well [4]. Stage of laser drilling When laser is contacted with surface of stone, under following stages stone is drilled respectively: spallation, melting and evaporating [3]. Upon contact of laser to surface of stone, laser shows the following reactions: beams are reflected, beams are distributed, beams are absorbed. [5] (Figure 4). Tests indicate that reflected, distributed and absorbed beams have low effect on stone, in fact mechanism that results in spallation and finally drilling rock, is absorbing laser beams [6]. Using laser in rock having high heat transfer coefficient results in evaporating accumulated crystal water with solution mineral materials at stone, expansion of stone and finally fractures made in structure of stone. In different tests it is used from laser working with nitrogen gas. Reason of using nitrogen gas is burning discharged gases during stone drilling and discharging vapor. This gas results in cleaning crushes. In rotating drilling it is used from transferring fluids from bottom of well to surface of well, meanwhile research in the field of laser drilling by presence of drilling fluid is continued [7]. Maybe one of the drilling parameter that is less attention is rate of penetration. Rate of penetration (ROP) is regarded as one of the fundamental factors in oil and gas well drilling, so that cost of drilling depends on this parameter. ROP is obtai ned from following equation: According to above relation, the unit of measurement of ROP is in accordance with cm/s which can be changed to ft/h. Actualy, the ROP has a direct relationship with the (SP) and have reversed with the (SE). In fact, SP is the power delivered to the laser system while SE is the amount of energy consumed for spallation of a given formation. As it is determined from the definition of SP, this parameter is calculated by the following relation : With consideration of same diameter of drilling for the each sample, the rate of SP is obtained w/cm 2 in this experiment. This rate is calculated on the basis of experimental present facilities. In order to gain SE given:

4 4 SPE/IADC Generally by using this method costs and working days of drilling rig is decreased. In this paper it is attempted to find out relationship between laser technology and oil and gas well drilling upon comparison of rate of rotating drilling, laser drilling, laboratory information and data. By using different tests, rate of drilling for each sample (Sandstone, Limestone and Shale) under saturated and non-saturated mode is achieved. Goal of these tests is obtaining real value of drilling rate in accordance with available equipments. Experimental setup Sample stones that are offered in this paper include: Sandstone, Limestone and Shale (Figure 5). Each of these three groups included three types of stones with different depth, porosity and saturation. Among each of these three groups, one sample stone is saturated by water for performing exact results and comparisons. For the first time CT scan machine is used in order to observe changes before and after laser working operation. CT scan machine Picker 1200 with 130KW voltage and current of 80MA during 2sec was used. All 9 samples gone under CT scan photographing and then samples were gone under drilling in laser laboratory. Laser system that is used in this laboratory worked with power of 700W and continuous wave mechanism (Figure 6). Laser system uses from its 100% power by rate of radiation nearly 10mm/s. In this test it was used from spiral mechanism for drilling in which stone was drilled for 66sec with diameter of 1cm. Then sample were again gone under CT scan photographing. Figure 7 indicates CT scan photos before and after laser working operation and then following observations was studied: Level of specific energy (SE), Rate of penetration (ROP), comparing rate of drilling and special energy for saturated and non-saturated samples, effect of purging gas on perforation depth, effect of laser drilling on drilling costs, and effect of laser drilling on environment management. Sample stones that were used in this test were selected highest number of formations which were found during drilling. Table 1 indicates physical properties such as: volume, weight and depth of sampling each stone. After saturating stones their properties such as, porosity and weight of saturation were measured that are offered in Table 2. As it was already mentioned, rate of penetration depends on two factors including, SE and SP. Value of SP upon fixed section of drilling for all samples (1cm) was nearly w/cm 2. Upon fixed value of SP and change at value of SE, rate of drilling for each sample of stone was different. SE depends on type of stone and physical properties of stone including: heat transfer coefficient, porosity, densit, and etc. Table 3 indicates specific energy and rate of penetration for each sample of stone after laser perforation. Result and Discussion Lavel of Specific Energy As it is observed in table 3, level of specific energy for drilling volume unit of Sandstone under nonsaturated mode is less in comparison to other samples. Special energy for Sandstone is nearly 32j/cm 3 to 36j/cm 3. This value for Limestone is 39j/cm 3 to 42j/cm 3 and for Shale is 42j/cm 3 to 45j/cm 3. Whereas specific energy depends on reflected, distributed or absorbed rays, it is inferred that level of absorbed rays is Sandstone is higher than other type of stones. Tests indicated that this issue for saturated samples is vice versa. Reason of this difference at special energy and consequently rate of penetration based on several factors is justifiable that is offered in future sections. Figure 8 obviously indicate this issue. Rate of Penetration After measuring rate of penetration for each sample of stone, it was indicated that the highest rate of penetration was related to Sandstone (Table 3). Tests indicate that highest displacement heat coefficient is related to Sandstone. As it was already mentioned, upon increasing heat transfer coefficient the microfracture of stone that are created due to laser radiation is also increased. Upon increasing these microfractures the rate of penetration is increased and time of drilling is decreased. In addition, increasing microfractures inside of stone matrix and its surface; results in increasing permeability of stone. In the

5 SPE/IADC present article it is used from low power laser 700W. Meanwhile, nowadays laser tests are performed with high power laser nearly 7000W. By improving power of system it is possible to increase rate of penetration. Figure 9 indicates comparison between rates of penetration for each of the sample stones under non-saturated mode. Comparing Rate of Penetration and Specific Energy for saturated and non-saturated samples As it is indicated from table 3, rate of penetration and value of SE for non-saturated samples is different with rate of penetration and value of SE for saturated samples. Range of specific energy for saturated samples like Shale is nearly 31j/cm 3, Limestone as 59j/cm 3 and Sandstone as 84j/cm 3. According to aforesaid values it is indicated that highest rate of penetration for saturated sample belongs to Shale, Limestone and Sandstone respectively. Importance of this issue is that in oil and gas well drilling, the highest level of drilling belongs to Shaly formations. Shale has much porosity but low permeability and its density is different in accordance with depth of water. According to Table 2 reason of this issue is due to saturation ratio of stone. As it is indicated from table, saturation of Sandstone is higher than Shale and keeps higher level of water in its structure. Therefore while radiation of laser on surface of Sandstone, power of laser is spent for evaporating water in structure of stone and transferred energy to stone is decreased, which results in decreasing rate of penetration in saturated samples in comparison to nonsaturated samples. Of course Shale is exception, since upon saturation of Shale the rate of drilling is increased, so that rate of laser drilling for saturated Shale is higher than rate of drilling non-saturated Sandstone. Figure 10 obvious indicates this issue. Effect of purging gas on perforation depth Experimental results gave some answers to regarding the purging improvement, application of Air pomp (Air amplifier) to remove rock cutting. Purging operation is important for cuttings removals and clear the path for the beam deliver to the rock. Dust, debris and cuttings from perforated hole will absorb the beams, therefore less energy will be delivered to the rock sample. In addition, these dusts caused for skin in perforated zone. Figure 11 shows actual laser cutting and dust from laser rock drilling. This photo magnified with camera about 12X. The purging method improved by adjusting the distance between purifying nozzle to the rock sample surface and the angle of purify and the flow pressure. The optimized angle was found to be 28 o - 40 o and the optimized distance from the target was 1 inch. In this experiment we encountered with limited facilities, so laser system and air pomp that using in this research had low power. However, by using this power we determined precision result. The angle and the distance were the most efficient in removing the dust and debris from perforation hole which allow the energy to be delivered to the formation. In ideal condition, if the purging is efficient, then the laser should create a typical hole identical to the shape of the beam, the hole created in the sample should match the shape of the beams. Effect of Laser Drilling on Environmental Pollution While drilling one well, many of the waste waters produced during drilling are incorrectly entered into nature cycle. Many of these waste waters are produced due to using old equipments and incorrect technologies. While during drilling it is used from oil based mud for drilling well, environment is greatly damaged, since this type of mud is mainly used for Shaly formation which is among dangerous chemical materials for environment. These chemical materials enter into environment nature due to drilling fluid alternate rotations. Upon entrance of laser system into oil and gas well drilling industry, many of these pollutions are decreased. In application of this system it is possible to use dust drilling, in which in this type of drilling instead of using oil based mud, it is used from air fluid for drilling. In addition level of produced wastes due to drilling is decreased, since due to replacement of electronic system with mechanical system instead of using heavy equipments such as heavy drilling pipes, it is used from light weight equipments which results in considerable decrease in environmental pollution.

6 6 SPE/IADC Effect of Laser Drilling on Cost of Drilling Cost of each foot drilling oil and gas well is obtained through following equation: As it is inferred from above formula, cost of drilling has vice versa relationship with length of drilling (F), so that while using laser system instead of drilling system, length of drilling by laser system is increased. Therefore great section of drilling cost is decreased. It seems that due to using electric energy instead of mechanical energy in laser system, level of damage during drilling is decreased which requires more research. In addition by using laser system, duration of working days of drilling rig, triping time for changing bit is decreased. Conclusion Using laser system instead of rotating drilling system in drilling industry has several advantages; however, these advantages depends on many parameters of laser and also type of laser. As it was indicated in this paper, by entrance of laser drilling system into oil and gas well drilling industry, we may observe considerable advance in this industry. It is to be noted that entrance of this system into drilling industry requires several field test and passing time. This task may be started by drilling specified layers, especially problematic layers and to develop and stabilize it upon passing time. By virtue of results it is observed that, increasing rate of stone drilling results in decreasing level of required energy for stone drilling [10]. In non-saturated samples, the highest rate of penetration was related to Sandstone and among saturated samples, the highest rate of penetration was related to Shale. Whereas most of the drilled formations of Iran were either Shale or Sandstone, it is possible to conclude that entrance of this system into drilling industry, results in great revolution at drilling industry. Due to limitation of present article, the tested samples were among three groups and consequently for having general conclusion it is possible to use other type of stone as: carbonate, dolomite, granite, ant etc which requires broad research and cooperation with related organization. It seems that using laser drilling while soil is loose and there is possibility of collapsing micro stones is not useful, since rate of rotating drilling in these sections is higher than laser drilling. In addition, according to excess radius of well at initial sections, level of required energy for stone drilling is increased and consequently rate of penetration is decreased. It seems that by using laser drilling in bottom layers which are full of micro drilling, dust and light weight, it is possible to use air fluids of micro drilling to direct dust created as a result of laser drilling toward out of well. Whereas dusts are directed toward outside through air, in order to transfer these dusts it is not used from oil based fluids which results in deceasing environmental pollution. With respect to other aspects it seems that fishing operation inside of oil and gas well may be improved by using laser. It is to be noted that this technology is useful when we are faced with small and unimportant fishs in which discharging them is not necessary. It is possible to melt these materials inside of well and continue drilling operation. Nowadays improving perforation operation of oil and gas well by using laser is being carefully investigated by oil engineers [11]. At the end it is necessary to mention that complete entrance of new technology into each industry, requires enough time and several tests. It is obvious that at the first entrance of any new technology, it is faced with some problems and deficiencies; however, by passing enough time and developing researches, it is possible to solve problem and stabilize new technology. Acknowledgement The authors would like to extend their thanks to Society of Petroleum Engineering Iranian section, specialy Mrs. Masoumeh Ahmadiani and would like to express our thanks to all of teachers for them helps in our research progressive and Dr. Gholam Hossein Montazeri.

7 SPE/IADC Nomenclature P e = External pressure, psi P wf = Bottom-hole flowing pressure, psi PI = Productivity index, bbl/day/psi q = Flow rate, STB/day µ = Viscosity, cp β = Formation volume factor, bbl/stb k = Permeability, md h = Thickness, ft r e = External radius, ft r w = Wellbore radius, ft s = Skin factor ROP = Rate of penetration, cm/s SP = Power per unit area, w/cm 2 SE = Amount of energy required to remove a unit of rock, w.s/cm 3 P avg = Average power of laser, w A r = Drilling area, cm 2 t = Time of radiation, s V r = Unit of drilling volume, cm 3 C t = Cost of every foot drilling, $/ft B = Cost of bit, $ C r = Cost of rig, $/h T = Bit life, h t = Stop times and tripping times, h F = Drilling length by every bit, ft Reference [1] R.M Graves, D.G O'Brien D.(1998) StarWars Laser Technology Applied to Drilling and Completion Gas Wells, SPE Annual Technical Conference and Exhibition, New Orleans, Louisiana, SPE [2] B.C. Gahan, Ricahad A. Parker, Sahim B, Humberto. F, Zhiyue X D.(2001) Laser Drilling: Determination of Energy Required to Remove Rock, SPE Annual Technical Conference and Exhibition,, New Orleans, Louisiana, SPE [3] R.M Graves, D.G O'Brien D.(1999) StarWars Laser Technology for Gas Drilling and Completions in 21 st Century, SPE Annual Technical Conference and Exhibition, Houston, Texas, SPE [4] P. Sihna, A. Gour D.(2006) Laser Drilling Research and Application: An Update, SPE/IADC Indian Drilling Technology Conference and Exhibition, Mumbai, India, SPE/IADC [5] M. Bakhtbidar, M. Ghorbankhani, M.R. Kazemi Asfeh, M. Alimohammadi, Laboratory Experiments Investigation of Effect of Laser Energy on a Variety Rock Types: An Exploration Innovative Technology, EarthDoc 10716, 73 rd EAGE Conference & Exhibition Incorporating SPE EUROPEC, Vienna, Austria, May 23-27, [6] R. Parker, Z. Xu, R. Graves, B. Gahan. (2003) Drilling large diameter holes in rocks using multiple laser beams, ICALEO conference in China, LIA 504. [7] Z. Xu, C. Reed, R. Graves, R. Parker. (2004) Rock perforation by pulsed ND:YAG laser, 23 rd PICALO conference in USA, LIA 138. [8] Z. Xu, C. Reed, R. Graves, R. Parker. (2004) Laser spallation of rocks for oil well drilling, 23 rd PICALO conference in USA, LIA 140. [9] N. Bjorndalen, H.A Belhaj, K.R Agha, M.R Islam. (2003) Numerical investigation of laser drilling, SPE Eastern regional in Pennsylvania, USA, SPE [10] S. Pooniwala. (2006) Lasers: The next bit, SPE Easteren regional in Ohio, USA, SPE [11] S. Batarseh, H. Figueroa, N. Skinner, Z. Xu. (2003) Specific energy for pulsed laser rock drilling, Journal of Laser Applications, Volume 15.

8 8 SPE/IADC Fig 1. Perforation job efficiency ( ) Fig 2. Shematic of laser perforated wellbore geometry Fig 3. Pressure distribution in a reservoir with a Skin

9 SPE/IADC Fig 4. Beams reaction when radiate on rock surface Fig 5. Rcok samples which drilling by laser, left to right: Limestone, Shale, and Sandstone Fig 6. Laser machine which used for laser perforation research Fig 7. X-Ray Computed CT Scan image from samples, before and after laser perforation

10 10 SPE/IADC Table 1. Rock samples physical properties ( * Saturated samples ) Table 2. Physical properties of saturated samples Table 3. Amount of ROP and SE after laser perforation

11 SPE/IADC Fig 8. Amount of Specific Energy for non-saturated rock samples Fig 9. Amount of Rate of Penetration for non-saturated rock samples Fig 10. Comparing ROP for no-saturated and saturated rock samples

12 12 SPE/IADC Fig 11. Rock cutting and dust which obtained from laser perforation operation