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    Productividad Productividad Document Transcript

    • SPE 69582Field Experiences in Evaluation and Productivity Improvement Using SelectiveHydraulic Fracturing in Deep Directional Wells. Orocual Field, VenezuelaG.A. Carvajal, SPE, K. Ortiz, PDVSA, A. Carmona, PDVSA, G. Parra, PDVSACopyright 2001, Society of Petroleum Engineers Inc. 15 % of the planned volume). The hydraulic fractures wereThis paper was prepared for presentation at the SPE Latin American and Caribbean Petroleum designed to be carried out in stages, in order to improve theEngineering Conference held in Buenos Aires, Argentina, 25–28 March 2001. production profile of the wells due to the high heterogeneity ofThis paper was selected for presentation by an SPE Program Committee following review ofinformation contained in an abstract submitted by the author(s). Contents of the paper, as the sands combined with a width of 670 ft in average that didpresented, have not been reviewed by the Society of Petroleum Engineers and are subject to not allow the best allocation of the proppant and slug.correction by the author(s). The material, as presented, does not necessarily reflect anyposition of the Society of Petroleum Engineers, its officers, or members. Papers presented atSPE meetings are subject to publication review by Editorial Committees of the Society ofPetroleum Engineers. Electronic reproduction, distribution, or storage of any part of this paper Field Descriptionfor commercial purposes without the written consent of the Society of Petroleum Engineers is Orocual Field is operated by Eastern PDVSA EyP through theprohibited. Permission to reproduce in print is restricted to an abstract of not more than 300words; illustrations may not be copied. The abstract must contain conspicuous North Unit Management Team, it is located 20 km West ofacknowledgment of where and by whom the paper was presented. Write Librarian, SPE, P.O.Box 833836, Richardson, TX 75083-3836, U.S.A., fax 01-972-952-9435. Maturin at the North of Monagas State in Venezuela. The San Juan Formation is part of the deep Orocual reservoirs and it represents around 80% the North Units total production. TheAbstract San Juan Formations developed area is divided into fourUntil 1998, eleven vertical wells had been drilled in Deep reservoirs, these are San Juan-03, 06, 07 and 09, allOrocual Field in Eastern Venezuela for a total of 16 hydraulically separated by sealing faults. The San Juancompletions to produce light oil and condensate. By stratigraphic column has been characterized and defined ashydraulically fracturing these wells, the productivity improved three different hydraulically connected flow units, Lower,up to three times compared to the initial rates. The use of new Middle and Higher San Juan (see Fig. 1). The reservoirstechnologies in drilling directional wells allowed the contained in the San Juan Formation are medium, light andconstruction of three of these wells wells in the San Juan condensate producers with variation of the composition of theFormation. fluids with depth. The average thickness of the Formation is This paper resumes the experiences associated to three 650 feet. The OOIP is estimated in 336411 stb. The reservoirswells in the Orocual Field, the evolution of operational have been described as volumetric and, to date, only one ofpractices and data acquisition that had to be implemented in them is subject to secondary recovery through gas injection.order to, in some cases, overcome the effect of early stagescreenouts and properly evaluate the productivity of such Geology and Tectonism. The structural model on top of thewells. Additionally said, experiences allowed the comparison San Juan Formation indicates an asymmetric anticline with,of the fracturing techniques applied in these case studies, with slightly steeper dips to the south related to thrusting from thethe conventional designs used in the past and to establish the north. The thrust sheet was subsequently cut by one left lateralbest evaluation and stimulation techniques for the San Juan shear fault, separating the Orocual Field into two distinctFormation wells. structures. The depositional environment was relatively uniform as indicated by a minimal grain size variation. TheIntroduction appearance of the San Juan Formation is a continuousThe drilling of new directional wells in Orocual Field meant a sedimentation in a transgressive system, with the initialreal challenge in the planning and design of the hydraulic deposition of clastic material, coarse type at the bottom andfracturing activities to be performed on these wells. Based on shale beds occurrences towards the top.an exhaustive study of the tectonics of the formation, the wells The maximum horizontal stress is oriented in North East-were drilled with 25 to 42 degrees from the vertical axis in the South East direction. As a result of the collision of thedirection of the minimum stress and in the direction of the Caribbean and South American Plates the Serranía del Interiormaximum stress, to and against the dip of the reservoirs. was formed. The maximum stresses have a preferential The initial design of the hydraulic fractures in the first direction of 170°. These structural styles make their statementwells was conventionally planned based on statistical behavior in the main fault patterns in which a pattern of 50 to 60° ofof the previous jobs. In some of the wells, the result was an direction is highlighted, and it corresponds to the direction ofearly screenout with little proppant entrance (between 10 and
    • 2 K. ORTIZ, G.A. CARVAJAL, A. CARMONA, G. PARRA SPE 69582the principal structural feature (inverse faults and anticlines) Perforating Designwith a subordinated direction of 15 to 20° corresponding to The conventional vertical wells were perforated to obtain thenormal faults. most contribution per foot of perforated sand, for this reason 100% of the net interval was perforated, including Lower,Drilling and Completion Middle and Higher San Juan Formation. This led to a non-Since 1990, fourteen wells have been drilled in the San Juan homogeneous production profile due to the non-selectivity ofFormation; seventeen of these are vertical wells with double the fracturing jobs. In these cases, the fracturing fluid and thecompletions. In the past two years, two directional wells, proppant were displaced throughout the intervals that offeredORC-29 and ORC-30, were drilled, in San Juan 06 and San less horizontal stress and higher permeability, which in allJuan 07 reservoirs, respectively. The most important cases, was the most shallow of the intervals and thus the onecharacteristics can be detailed in Table 1. with the highest GOR and nearest to the gas-condensate cap. In search of the best fracture and productivity results, the This non-effective production profile attempted against adrilling design was made based upon the highest natural rational production of the San Juan reserves.vertical fracture distribution and the direction of the minimum An initial conventional perforating design was establishedhorizontal stress. A solid-free drilling fluid was used in 7 and for the deepest interval (zone 1) of Lower San Juan in ORC-294-1/2" holes. This fluid provided excellent drilling conditions well (see Fig. 5). During the first Fracture treatment, on thissuch as drilling rate, hole stability and adequate rheologic particular interval, there was an early stage screenout,behavior; it also allowed the use of a fluid with density of 9.5 presumably due to the formation of multiple fractures thatppg, representing 2.5 ppg less than the usual 11.5 ppg used in inhibited the proppant entrance in the formation. Since thisother San Juan wells. was the only case in San Juan fracturing history and one of the The direction and incline of the wells were established most deviated wells on the field, the theory of the formation ofconsidering the dip of the geological structure, the direction of multiple fractures led to the redesign of the perforatingthe minimum horizontal stresses and the distribution of the techniques and methodsformations natural fractures. Due to numerous operational andproduction problems presented by double completions and a Shot Hole Phas Type Selectionnew characterization of the reservoir, as three hydraulically density Diameter ecommunicated flow units, a 4-1/2"monobore completion Conventional 100 % 6 spf 0,25 inch 60°design was employed on these new directional wells. Figure 2 Redesign 10 feet 12-18 spf 1,1 inches 60°shows an example of the direction and incline of the wells. The perforating of 10 feet of the net pay and the increaseGeomechanical Model of the Reservoir of the shot density and hole diameter in some cases propitiatedSan Juans geomechanical model allowed the description of some control of the mitigation of multiple vertical fracturesthe stresses and the characterization of natural fractures. The and high tortuosity effects.existence of natural fractures in highly consolidatedsandstones (Cf = 6*106 1/psi), specifically in San Juan, has Hydraulic Fracturing Designbeen broadly documented in studies and special core analysis, After the selection of the intervals, it was important toimage logs, and fluid loss studies. The geomechanical studies consider the elastic and petrophysical characteristics of thehave proved a variation in the direction of the horizontal rock. These were measured with special logs such as Crossed-stresses of the formation and the nature of the natural Sonic Dipolar and Spectral Gamma Ray. The following datafractures. The natural fracture analysis and the regional was obtained from the processing of these logs:tectonics support a direction of the minimum stress as N35°Wwith parallel open fractures toward this direction and closed Youngs Modulus = 5,4*10-6 psiones in perpendicular direction. Poissons Ratio = 0.2 The formations stress field presents a normal regime Porosity = 6%where the higher stress is the vertical (σv = 1-1,1 psi/ft) and Permeability = 5 mDthe intermediate and minor stresses correspond to the Rock Compressibility = 6*10-6 psi-1intermediate horizontal stress (σH =0,68 psi/ft) and minimum Invasion radius = 45 fthorizontal stress (σh=0,65 psi/ft). Temperature = 275°F The stress field map is shown on Figure 3 where the Net Pay = 50 -220 ftdirection and magnitude of the horizontal stresses can be Vertical Stress = 1-1,28 psi/ftobserved. The directional wells were drilled toward the Horizontal Stress = 9250 psiminimum stress in order to reduce the drilling days andoperational costs (see Fig. 4). In order to prevent early screenouts and assure the success of the fracturing job, 10 feet of the net pay were selected; the choice was based on the best elastic characteristics such as a
    • FIELD EXPERIENCES IN EVALUATION AND PRODUCTIVITY IMPROVEMENT USING SELECTIVESPE 69582 HYDRAULIC FRACTURING IN DEEP DIRECTIONAL WELLS. OROCUAL FIELD, VENEZUELA 3Youngs Modulus between 1.2 and 6.8*106 psi and a Poissons Pore Pressure, psi 7500-6300Ratio from 0.1 to 0.25 Fracture Gradient, psi/ft 0,43-0,6 The vertical and horizontal stresses were determined by Depth, ft 14000-16000the following equations: Average bauxite concentration 3,5 Total bauxite, pounds 40.000σv = 0,007 * ρ * D − Pr ……………………………….(1) Average Conductivity, mD-ft 30.000 ν Bauxite size, mesh 20/40σH = (σv − Pr ) …………….……………………..(2) Pumping rate, bpm 20 1 −ν Max. Pumping pressure, psi 10.200Practical Design Considerations. In very low horizontal Frac. Dimensions (xf, hf, wf), ft 100, 100, 0,2permeability and very heterogeneous reservoirs, like San Juan,(Kv = 0.2 mD, Kh = 5 mD) hydraulic fracturing in stages is Formation Evaluationvery important. This technique consists in fracturing, from The evaluation of the wells followed the same procedure forbottom to top, each prospective interval separately, isolating the most detailed and economical friendly characterization ofthe fractured zones after each stimulation. Also, for thick San Juan 07 and San Juan 06. The first pre-evaluation stepsands, it is recommended to perforate only from 5 to 15 ft of was a compilation of the existing information of the reservoirsthe net pay before the stimulation to have better control of the that led to a jerarchical organization of the new informationfracture and then connect the stimulated formation by required for the new wells. Typical evaluation techniques wereperforating the remaining feet with high penetration shots (see used, such as:Figure 6). In deviated wells, it is difficult to achieve this Buildup Tests. Layer reservoir parameters, such asconnection, which makes it hard to perform this technique permeability and formation damage, were obtained fromsuccessfully. One helpful practice is to locate the perforations pressure transient analysis of build up tests. These tests werenear the top op the shale seal in order to induce the growth of conducted before and after hydraulic fracturing for both initialthe hydraulic fracture from bottom to top. characterization of permeability, skin and reservoir pressure In naturally fractured reservoirs like San Juan, avoiding to and the resulting parameters after hydraulic fracturing; specialperforate in zones with natural fractures oriented towards the attention was given to formation damage values in order tomaximum stresses has been noted to help prevent early stage evaluate the effectiveness of the stimulation jobs.screenouts during hydraulic fractures. Production Logs. Production logs were used after each In order to obtain a more homogeneous production profile fracturing treatment to obtain information of productionand a better fracture the perforated zones were chosen taking profiles of the wells after each fracturing job.in account the zone with the lowest permeability. Also, using PVT Sampling. Three PVT samples, one bottomhole andthe Neutron Density Logs, the high GOR and gas intervals two surface samples were taken as part of the characterizationwere identified and avoided to minimize the gas production of both San Juan 06 and 07.and optimize the bottom light oil contribution. The approach used in these cases was to obtain initialStimulation Treatment. The dimensional design of the reservoir parameters from pressure transient analysis that werefractures pursued the following characteristics: xf = 90 ft ; Hf compared and validated with previous core, petrophisical and= 10 ft ; ω= 0,2 inches. The fracture was designed to transient analysis. The evaluation of the fracture jobsovercome the invaded and damaged zone, the Geerstma- performance was achieved through production log tools toDeklerk equation was used in order to calculate xf. quantify the fluids and the quality of the production profile after all the stages of the fractures and perforations were finished.xf = E * w p …………………………………………...(3) Field Experiences and ResultsTo achieve a length of 90 ft, the fracturing pressure design ORC-29 Well. This well was drilled to produce light oilwas 9200 also from the Geerstsma-Deklerk equation: reserves of San Juan 06 reservoir. The initial evaluation and stimulation design consisted in three hydraulic fractures, twop = ( E 3 * µf * qi )1 / 4 / (hf 1 / 4 * xf 1 / 2 )……………….(4) in Lower San Juan and one in Higher San Juan Lower San Juan.The conductivity of the fracture was obtained from equation 5: Zone 1. 43 feet of the deepest sand were perforated with 6 shot per foot density. The well produced 190 stb/d with a choke of 1/4". The initial build-up test showed a typical San kf * ωCdf = ……………………………………………(5) Juan Formation value of skin and permeability ranging from 5 k * xf to 9 mD and a skin factor of 35. For this well, it was possible to use bottomhole shutdown to reduce the effects of wellboreThe general design of the fractures was as shown: storage for more accurate and reliable results.
    • 4 K. ORTIZ, G.A. CARVAJAL, A. CARMONA, G. PARRA SPE 69582 The hydraulic fracture was made with a pumping rate of the fact that in deviated wells, it is hard to connect the30 bpm with a 3 ppa proppant concentration. Once the surface fractured interval with the wellbore by perforating thepressure reached 10000 psi, the fracture was suspended due to remaining zones using conventional practices.an early stage screenout. Only 20 sacks of proppant could be Results did not show the increase of production that waspumped into the formation. After this first hydraulic expected by adding one of the most prospective zones of thefracturing, the well produced 520 stb/d with the same choke well when it is compared with the same choke diameter. Thisdiameter. can be explained by the known compositional variation of the As noted before, on the perforation design section, it is fluid with depth that caused an increase on the GOR, mainlypresumed that the early screenout was due to the formation of in Middle San Juan, when the fracture job and perforationsmultiple fractures, which inhibited the proppant entrance in contacted the higher part of the structure.the formation. This brought a about redesign of the perforatingtechnique being applied. ORC-30 Well. This well was drilled to produce gas Zone 2: Only 10 out of a total of 47 feet of sandstone were condensate (46° API) reserves of reservoir San Juan 07. Theperforated with a shot density of 12 spf. The previous original evaluation design consisted in hydraulically fracturingfractured zone (zone 1) was isolated with a gravel plug. Zone three zones, one in Lower San Juan and two in Middle San2 was fractured with a pumping rate of 18 bpm. 1272 barrels Juan.of fracture fluid were pumped with 342 sacks of proppant Lower San Juan. For this case only 5 feet of a total of 7920/40 at a maximum surface pressure of 7400 psi. of Lower San Juan Formation was perforated for the fracturing Zone 3: Considering the success of the previous job, zone job. Initially it produced 300 stb/d with a choke of 1/4" and1 and 2 were isolated and 10 of the 43 remaining feet of there were no representative measures of permeability andLower San Juan were perforated. The surface pressure raised skin due to operational problems during the bottomhole shutto 10660 psi and premature screenout occurred rapidly at the down of the well. For the fracture, 410 sacks of 20/40beginning of the fracturing job; only 22 sacks of proppant proppant were placed in the fracture reaching a surfacewere pumped into the formation. This second failure of the pressure of 9200 psi. Due to the poor rock quality of the zonefracturing job is presumed to have been motivated by a high (5.6 mD and 5.8 % porosity), the small height of theconcentration of natural fractures located exactly on the ten perforated interval, and the small diameter of holes; theselected feet. These fractures were oriented towards the pumping of the fracturing fluid was qualified as risky becausedirection of the minimum stress, generating excessive of the high pressures reached during the fracture. This led totortuosity. the search of new or different technologies to diminish these For production profile characterization, two sets of effects.production logs were run, one to quantify the contribution of The total production of the well, after the fracturing job,Lower San Juan by itself, and the other after adding the was 450 stb/d.Middle San Juan Layers. Lower San Juan alone, achieved Middle San Juan.1203 stb/d with a highest choke diameter of 3/8". The Zone 1. Based on the experience on previous intervals andProduction log showed a production profile with very low well ORC-29, a high pressure and high penetration type ofcontribution from zone 1 and zone 3. It is interesting to note perforation was used on six feet of a total of 108 feet ofhow zone 1, after having produced alone 520 stb/d post Middle San Juan Formation. During the fracturing job, onlyhydraulic fracture, ended up having almost zero production 159 of the 400 planned sacks of bauxite 20/40 were placed at aafter activating the well with all of Lower San Juan. The entire maximum rate of 20 bpm and a maximum surface pressure ofproduction of the well came from zone 2 and four added 10600 psi. Screenout occurred an it is presumed that theintervals above and below this zone. creation of multiple fractures caused the screenouts due to the Middle San Juan. Only the lowest interval of Middle San high deviation angle of the well (42°).Juan was fractured at this stage in order to avoid contacting After this second stimulation and the perforation of 102 fthigher GOR zones or a gas cap. From the interpretation of the of Middle San Juan, the production of the well rised to 730sonic dipolar and image logs, 10 feet in a zone with low stb/d.natural fracture density and near the top of a shale seal were Zone 2. Changing in this occasion all the procedures usedchosen. The result was a maximum surface pressure during the in previous jobs, 34 ft were perforated with a shot density offracture of 7200 psi and a placement of 297 sacks of proppant 18 spf. The fracture job was done at a pumping rate of 30into the fracture. Afterwards, 95 remaining feet were bpm and a maximum surface pressure of 8500 psi. Once thisperforated to complete the whole Middle San Juan interval. pressure was reached, screenout occurred achieving to place The final production log profile was run with different only 235 of a total of 400 sacks of proppant into the fracturechoke diameters, from 3/8" to 3/4", obtaining a total After the addition of the remaining intervals in Middle Sanproduction of 4000 stb/d with a fairly homogeneous Juan, the well reached a total production of 860 stb/dproduction profile. It is important to highlight that very littleproduction was obtained from the added perforated intervalsthat were not directly stimulated by the fractures. This proves
    • FIELD EXPERIENCES IN EVALUATION AND PRODUCTIVITY IMPROVEMENT USING SELECTIVESPE 69582 HYDRAULIC FRACTURING IN DEEP DIRECTIONAL WELLS. OROCUAL FIELD, VENEZUELA 5Conclusions 30428, presented at the 1995 Annual Technical 1. In low permeability and very heterogeneous Conference and Exhibition, Dallas, U.S.A., October 22- reservoirs, hydraulically fracturing in stages is 25. recommended as a common procedure. 4. Kogsboll, H.H., Pitts, M.J., and Owens, K.A. "Effects of 2. In naturally fractured reservoirs like San Juan, Tortuosity in Fracture Stimulation of Horizontal Wells - avoiding the perforations in zones with high A case Study of the Dan Field". Presented at meeting concentration of natural fractures has been noted to held at Offshore Europe held in Aberdeen, Scottland, help prevent early stage screenouts during hydraulic September 7-10 1993. fractures. 5. Strubhar, M. K, Fitch, J. L. , Glenn, E.E.. "Multiple, 3. The selection of the zones to perforate prior to the Vertical Fractures from an Inclined Wellbore - A Field fractures has to be made taking in account the zones Experiment". Presented at the SPE-AIME 49th Annual with the lowest permeability an nearest to the top of Fall Meeting, Houston, October 6-9. shally barriers. 4. In deviated wells, little production increase is obtained from added perforated intervals that are not directly stimulated by hydraulic fractures.Nomenclature ρ = oil density gravity σH =maximun horizontal stresses, psia σh =minimum horizontal stresses, psia σv =maximun vertical stresses, psia D=depth, ft Pr=pore pressure, lpc v=poissons ratio P=maximun pump pressure, psia Xf= fracture half-length, ft E=Youngs elastic module, psi w=fracture width, ft µf=fluid fracture viscosity, cp qi=fluid pumped rate, bpm hf= fracture thickness,ft Cdf=adimensiotal fracture conductivity Kf= fracture permeability,mD k= reservoir permeability,mDAcknowledgmentsThis paper reflects the work of a large number of people whohave contributed to the accomplishment of the initialevaluation of the new San Juan wells. The authors would liketo thank the management of the North Exploitation Unit,PDVSA for their support on the decisions made throughoutthe completion and evaluation process of the wells.References1. Economides, M., Hill, A. D, Ehling-Economides, C. Petroleum Production Systems. Prentice Hall, Inc. EnglewoodCliffs, New Jersey. 1994.2. Hagist, P., Harry, J., Abass, H., Hunt, J. And Besler, M..: "A case History of Completing and Fracture Stimulating a Horizontal Well" SPE 29443, presented at the 1995 Western Regional Meeting. Bakersfield, U.S.A, March 8-10.3. Hainey, B.W., Weng, X., and Stoisits, R.F.: "Mitigation of Multiple Fractures from Deviated Wellbores" SPE
    • 6 K. ORTIZ, G.A. CARVAJAL, A. CARMONA, G. PARRA SPE 69582 Table 1: Drilling and Completion Characteristics of wells ORC-29 and ORC-30 Casing Well Mud Depth Deviation Azimut Completion Design 20, Aceite 13-3/8, 9- 14898’- ORC-29 vassa 9,2 20° 277,8° Monobore 5/8, 15161’ ppg 4-1/2 20, Aceite 13-3/8, 9- 16448’- ORC-30 vassa 9,2 42° 115° Monobore 5/8, 15156’ ppg 7 Table 2: Fracturing an Production Results ORC-29 ORC-30 zone 1 zone 2 zone 3 zone 4 zone 1 zone 2 zone 3 Pumping Rate, bpm 30 18 18 20 25 20 20 Total Saks 21 342 22 297 410 159 235 Early Screenout YES NO YES NO NO YES YES Oil Rate before 190 NA NA NA 300 NA NA Stimulation, stb/d Oil Rate after 520 1200 1350 1600 450 730 830 Stimulation, stb/d Stimulation Radius, ft 13 95 20 110 120 37 89 Maximum Pumping 10600 7400 10300 7200 9200 10600 8500 Pressure, psi Closing Pressure, psi 10000 3500 7900 6500 6500 6450 8500 Perforated Interval 43 10 10 10 5 6 34 length, ft Shot Density, spf 6 12 12 18 18 18 18
    • FIELD EXPERIENCES IN EVALUATION AND PRODUCTIVITY IMPROVEMENT USING SELECTIVESPE 69582 HYDRAULIC FRACTURING IN DEEP DIRECTIONAL WELLS. OROCUAL FIELD, VENEZUELA 7 EDAD FO RM AC ION PLEIS TO CEN O M ES A FORMACION SAN JUAN PLIOCE NO LAS PIEDRAS 3000’ SAN JUAN 6600’ SUPE RIOR M IOCE NO CAR APIT A 10000’ SAN JUAN ARE O MED O I LOS OLIG OC ENO J AB ILLOS 12000’ EO CEN O CAR ATAS 13000’ PALEOC ENO V IDO ÑO SAN JUAN INFER OR I CR ET ACICO S AN J UAN 14000’ Fig. 1: Orocuals Stratigraphic Column with highlight on San Juan Formation Induced Fractures ORC-29 ORC-30 N S Natural Fractures ORC-29 ORC-30 Vertical Well Deviated Well Fig. 2: Example of the incline and direction of wells Fig. 3: Seismic line in direction of the dip of the structure
    • 8 K. ORTIZ, G.A. CARVAJAL, A. CARMONA, G. PARRA SPE 69582 Fig. 4: Maximun Stresses Direction from Crossed Sonic Dipolar and Minimus Stresses where are directioned the breakouts •EFFECTS: σ •Limited Entry. •Tortuosity Effects. 1Máx •Multiple Fractures. σ HMáx σ Min 100 % perforated interval •Low shot density. •Small Holes. •100% perforated interval. Sreenout Fig. 5: Conventional perforating design, resulting in formayion of multiple vertical fractures and early screenout
    • FIELD EXPERIENCES IN EVALUATION AND PRODUCTIVITY IMPROVEMENT USING SELECTIVESPE 69582 HYDRAULIC FRACTURING IN DEEP DIRECTIONAL WELLS. OROCUAL FIELD, VENEZUELA 9 Fracture Propagation Selected Interval •High shot density > 18 spf •Big Holes >1,2” •Few perforated feet Fig. 6: Perforating design used after redesign. DIFERENCIA DE ENERGÍA STONELEY SÓNICO DIPOLAR CRUZADO Fig. 7: Stonely wave and crossed sonico dipolar show fracture density zone high
    • 10 K. ORTIZ, G.A. CARVAJAL, A. CARMONA, G. PARRA SPE 69582 Fig. 8: Point select in order to perforating, can see the directions toward maximun stresses of the nature fractures