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A Feasibility Investigation of Hydra-jet Fracturing in Deep Wells

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A Feasibility Investigation of Hydra-jet Fracturing in Deep Wells
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  This article was downloaded by: [University of Oklahoma Libraries]On: 12 December 2012, At: 18:21Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registeredoffice: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Energy Sources, Part A: Recovery,Utilization, and Environmental Effects Publication details, including instructions for authors andsubscription information:http://www.tandfonline.com/loi/ueso20 A Feasibility Investigation of Hydra-jetFracturing in Deep Wells G.-S. Li a  , Q. Xia a   b  , Z.-W. Huang a  , H.-N. Qu a  , S.-C. Tian a  & M.Sheng aa  State Key Laboratory of Petroleum Resource and Prospecting,China University of Petroleum, Beijing, P.R. China b  CNOOC Research Center, Beijing, P.R. ChinaVersion of record first published: 27 Sep 2012. To cite this article:  G.-S. Li, Q. Xia, Z.-W. Huang, H.-N. Qu, S.-C. Tian & M. Sheng (2012): AFeasibility Investigation of Hydra-jet Fracturing in Deep Wells, Energy Sources, Part A: Recovery,Utilization, and Environmental Effects, 34:23, 2156-2163 To link to this article: http://dx.doi.org/10.1080/15567036.2011.561667 PLEASE SCROLL DOWN FOR ARTICLEFull terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditionsThis article may be used for research, teaching, and private study purposes. Anysubstantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,systematic supply, or distribution in any form to anyone is expressly forbidden.The publisher does not give any warranty express or implied or make any representationthat the contents will be complete or accurate or up to date. The accuracy of anyinstructions, formulae, and drug doses should be independently verified with primarysources. The publisher shall not be liable for any loss, actions, claims, proceedings,demand, or costs or damages whatsoever or howsoever caused arising directly orindirectly in connection with or arising out of the use of this material.   Energy Sources, Part A , 34:2156–2163, 2012Copyright © Taylor & Francis Group, LLCISSN: 1556-7036 print/1556-7230 onlineDOI: 10.1080/15567036.2011.561667 A Feasibility Investigation of Hydra-jetFracturing in Deep Wells G.-S. LI, 1 Q. XIA, 1;2 Z.-W. HUANG, 1 H.-N. QU, 1 S.-C. TIAN, 1 and M. SHENG 1 1 State Key Laboratory of Petroleum Resource and Prospecting, ChinaUniversity of Petroleum, Beijing, P.R. China 2 CNOOC Research Center, Beijing, P.R. China Abstract  With the exploration and discovery of deep low-permeability reservoirsin China, fracturing operations in high-temperature and deep wells are more and more important. Conventional fracturing treatment has some difficulties, such ashigh bottomhole fracturing pressure, high pump pressure, and malfunction of packer resulting from high temperature, etc. This article presents hydra-jet fracturing, aunique, relatively new stimulation technology that could greatly decrease bottomhole fracturing pressure,and pack off fracture interval using hydrodynamic energy without any packers, implementing fixed directional multilayer fracturing with a one-trip fracturing string. These technical advantagesof hydra-jet fracturing are conducive todeep wells fracturing. Keywords  deep wells fracturing, feasibility, fracturing pressure, hydra-jet fracturing,parameters calculating 1. Introduction Western exploration has now reached nearly 8,000 m. Abundant low permeability reser-voirs have been founded in Tarim and Junggar basins in which the main lithology is oncarbonate and tight clastic rocks, and depth, in general, is between 5,000–6,500 m. Theseoilfields have features, which include deeply buried, large thickness, high temperature,low permeability, strong heterogeneity, low natural productivity, and needs to apply acidfracturing and hydra-jet fracturing.High temperature and deep formation fracturing exists in a series of difficulties, suchas high temperature, high pressure, and high closure pressure, causing technical problemsas follows: (1) Target fracturing layers are deep, bottom formation fracture pressure ishigh, and the pipe friction loss will increase with the well depth increasing, so the groundfracturing construction pressure is high. (2) The high temperature formation fracturingfluid requires the properties of good heat resistant, anti-shearing, delay-crosslinking, andlow friction, meanwhile, the downhole sealing also needs good high temperature resistantperformance. (3) The operation well sections are deep, and formation closure pressureis high. Address correspondence to Hong-Na Qu, State Key Laboratory of Petroleum Resource andProspecting,University of Petroleum, Beijing, Beijing 102249,China. E-mail: bjquhongna@qq.com 2156     D  o  w  n   l  o  a   d  e   d   b  y   [   U  n   i  v  e  r  s   i   t  y  o   f   O   k   l  a   h  o  m  a   L   i   b  r  a  r   i  e  s   ]  a   t   1   8  :   2   1   1   2   D  e  c  e  m   b  e  r   2   0   1   2   Hydra-jet Fracturing in Deep Wells 2157  Due to the above difficulties of high temperature deep formation fracturing, thefracturing effect is limited in these reservoirs, using the conventional acid-fracturingtreatment; therefore, it is necessary to research a new acid-fracture technology. The hydra- jet fracturing technique is a new stimulation method that integrates with perforating,hydra-jet fracturing, and hydrodynamic sealing, and can fracture accurately set-pointswithout mechanical packers. Through hydraulic jetting, oriented sandblasting perforatingcan reduce formation of fracture pressure, so the fracturing measures can be effectivelyapplied in deep reservoirs of high temperature. 2. Hydra-jet Fracturing Mechanism  2.1. Hydraulic Sandblasting Perforating Mechanism Hydraulic sandblasting perforating is explained as follows: abrasive fluid is pumped downthrough a jetting tool, which converts high pressure energy into kinetic energy, then theabrasive jet begins to cut across the casing and cement sheath, thus, creating certaindiameter and depth perforation tunnels towards the reservoir rock near the wellbore(Song et al., 2006). Compared with conventional shaped charge perforation, hydraulicsandblasting perforating technology has the main properties of low perforating density,large hole diameter, deep-perforation, and easy location, etc. It can create spindle holeswith a large diameter of up to 50 mm and a depth of 800 mm in the formation withoutgenerating crushed zone (Gong et al., 2007; Liu and Li, 2006).  2.2. Hydra-jet Fracturing Mechanism According to the Bernoulli equation stating that jet tools generate a high-speed flow,the energy focusing on the pin-point begins to perforate and fracture (Eberhard et al.,2000; Tian et al., 2008). At the hydra-jet stage, by opening the tubing-casing annular,the perforating fluid injects into the formation and creates spindle holes in the formationin 15–20 min.At the hydraulic fracturing stage, close the casing-tubing annular or pump fracturingfluid into tubing annular, meanwhile, control annular pressure below fracture extensionpressure, and continue to inject fracturing fluid, which will form pressure boostingin the cavity. When the jetting boosting pressure and annular pressure are folded toexceed fracture pressure, then the top formation of the perforating hole begins to split(Figure 1). Actually, the boosting effect ensures the jet to realize the pin-point fracturing;the conditions are as follows: p boost  C p annulus  p f   :  (1)  2.3. Hydrodynamic Sealing After forming cracks, the high speed jetting fluid continues to inject into the cavity andcracks, so the jet nozzle, annulus, cavity, and cracks constitute a jetting system, whichacts just like a jet pump (Surjaatmadja et al., 2002). According to the Bernoulli equation,the jetting speed is high and the pressure is low near the outlet, thus, the annular fluidcan be drawn into fractures by the differential pressure, but is incapable of flowing toother places along the wellbore. So, the hydra-jet fracturing perforating process couldnot use the mechanical packers.    D  o  w  n   l  o  a   d  e   d   b  y   [   U  n   i  v  e  r  s   i   t  y  o   f   O   k   l  a   h  o  m  a   L   i   b  r  a  r   i  e  s   ]  a   t   1   8  :   2   1   1   2   D  e  c  e  m   b  e  r   2   0   1   2  2158 G.-S. Li et al. Figure 1.  Graphics of hydra-jet fracturing mechanism. (color figure available online) 3. Assembled Hydra-jet Fracturing Tool The assembled hydra-jet fracturing tool is the key part of this technique, which consistsof a centralizer, spray gun, one-way valve, and sieve tube (Figure 2).Some nozzles are fixed in the jet body, and according to the demand of the formationstress, the phase angle of nozzles can be optimized. A reflux device is part of the maintools, which is installed inside a seepage baffle and a ball at the bottom. The ball staysin the bottom when applying the hydra-jet fracturing operation, so the fluid will not flowfrom the bottom to annular. Fluid will flow through annular returning to the ground whenoperating reverse wash. 4. Hydra-jet Fracturing Feasibility Analysis in Deep Wells Hydra-jet fracturing technology integrated hydraulic sandblasting perforating and thehydraulic fracturing process. According to the demand of the formation stress, optimizethe phase angle of the nozzles and make sure the extension of cracks direction is inline with the direction of maximum horizontal principal-stress; avoid cracks in the nearwellbore reverse bend. Compared with conventional perforating, it can greatly reduceformation initial pressure, which effectively solves the problem of high initial pressure inthe deep well. At the same time, hydraulic sandblasting perforating creates large diameter Figure 2.  An assembled hydra-jet fracturing tool. (color figure available online)    D  o  w  n   l  o  a   d  e   d   b  y   [   U  n   i  v  e  r  s   i   t  y  o   f   O   k   l  a   h  o  m  a   L   i   b  r  a  r   i  e  s   ]  a   t   1   8  :   2   1   1   2   D  e  c  e  m   b  e  r   2   0   1   2   Hydra-jet Fracturing in Deep Wells 2159 holes. According to Hainey et al. (1995), flow resistance formula in holes is as follows: P   perf   / Q 2 c 2 d  4 N  2p ;  (2)where  P   perf   is hole flow resistance;  Q  is flow rate;  c  is flow coefficient;  d   is holediameter; and  N  p  is hole number.According to the formula, hole flow resistance increases gradually with the increaseof flow rate when a hole diameter is small. In order to balance the extra fracturing fluid, itis hard to develop extra tiny cracks near the wellbore. Therefore, it is very advantageousto use hydraulic sandblasting perforating to create a single main crack. In addition, usinghydraulic sealing in the entire process without using other packers can solve the failureof a packer in the deep and high temperature formation when applying fracturing.When the formation fracturing pressure is high, using the hydra-jet acid fracturingtechnique to pre-treat in carbonate formation can effectively solve the problems of asmall injection rate in regular acidizing and high well-head pressure. Hydra-jet fracturingtechnology can quickly form high quality foam acid in the bottom, and, finally, it gets agood acid fracturing effect. 5. Hydra-jet Fracturing Calculating Analysis in Deep Wells A casing completion well with a depth of 6,110 m and a well structure is shown inTable 1. Plan to apply the hydra-jet fracturing stimulation measure in the 4,500 m layer,and the formation fracturing gradient pressure is 0.024 MPa/m. The fracturing stringparameters are shown in Table 2.  5.1. Fracturing String Strength Check The hydra-jet fracturing string suffers mainly by the axial tensile force, so use the safetyfactor method to check axial tensile strength for the string joint. At different stagesof fracturing, the component of axial tensile force is also different. The stress of theoperating conditions is as follows:(1) Before applying hydra-jet fracturing: string likes a suspension chain, the wholestring suffers floating gravity.(2) At the stage of hydraulic sandblasting perforating: fluid flows into tubing, outfrom annular. String suffers floating gravity, the fluid viscous friction, and ex-pansion force.(3) At the stage of hydra-jet fracturing: fluid pumps into tubing and annular simulta-neously. String suffers floating gravity, the fluid viscous friction, and expansionforce, but the difference is that string suffers the friction from fluid in tubingand annular.In order to guarantee the safety of string in each stage in the process, it is necessaryto consider the most dangerous situation that string suffers float gravity, fluid viscousfriction, and expansion force.According to Table 2, the calculating results are as follows (Du et al., 2008): thefirst section tubing in vertical deep 2,000 m suffers the biggest axial tensile force T1,T1 D 404 : 8 kN :    D  o  w  n   l  o  a   d  e   d   b  y   [   U  n   i  v  e  r  s   i   t  y  o   f   O   k   l  a   h  o  m  a   L   i   b  r  a  r   i  e  s   ]  a   t   1   8  :   2   1   1   2   D  e  c  e  m   b  e  r   2   0   1   2
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