Available online at http://ijcpe.uobaghdad.edu.iq and www.iasj.net Iraqi Journal of Chemical and Petroleum Engineering Vol.20 No.1 (March 2019) 49 – 52 EISSN: 2618-0707, PISSN: 1997-4884 Corresponding Authors: Khalid Hazem Hassan, Email: Eng.khalid.1994@gmail.com , Hassan A. H. Abdul Hussien, Email: Hahah692000@yahoo.com IJCPE is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License. Estimation of rock strength from sonic log for Buzurgan oil field: A Comparison study Khalid Hazem Hassan and Hassan A. H. Abdul Hussien University of Baghdad-College of Eng/ Dept.of Petroleum Eng. Abstract It is very difficult to obtain the value of a rock strength along the wellbore. The value of Rock strength utilizing to perform different analysis, for example, preventing failure of the wellbore, deciding a completion design and, control the production of sand. In this study, utilizing sonic log data from (Bu-50) and (BU-47) wells at Buzurgan oil field. Five formations have been studied (Mishrif, Sadia, Middle lower Kirkuk, Upper Kirkuk, and Jaddala) Firstly, calculated unconfined compressive strength (UCS) for each formation, using a sonic log method. Then, the derived confined compressive rock strengthens from (UCS) by entering the effect of bore and hydrostatic pressure for each formation. Evaluations the result of compared rock strength generated from two wells for the same formation and match the bottom and top of this formation in two wells. Based on the obtained results, a good agreement between values of unconfined compressive strength from well (50) and well (47) that used real along of drilling section. The net results of the match between rock strength for wells (BU-50, BU- 47) of five formations; Mishrif, Sadia, Middle lower Kirkuk, upper Kirkuk, and Jaddala were 97, 87, 96.5, 97, 86 %, respectively Keywords: drilling, unconfined rock strength, sonic log Received on 18/11/8102, Accepted on 16/01/8109, published on 30/03/8109 https://doi.org/10.31699/IJCPE.2019.1.7 1- Introduction The value of rock strength for each foot of the well, from the surface to the bottom of the hole, is very difficult to be achieved. For example, it is difficult to get the safe density for drilling fluid during the drilling of the different formations to avoid instabilities of the wellbore and when design the program of casing ‎[1]. It is very essential for a drilling engineer to know all the data associated with the strength of rock along the well because the production of sand during extraction of oil is also great degree depending on lithology of reservoir or strength of the rock. Also, the penetration rate and wear of bit largely depend on the value of rock strength, where an increase in strength of rock led to increased wear of drilling bits and decreased penetration rate which increases the cost of drilling ‎[2]. Several methods are used to calculate the strength of rock for each foot during the drilling process. First, we can calculate the strength of rock directly in the lab via a mechanical method on cutting or cores. In addition, the strength of rock can be calculated from log data which achieved during the drilling process by using sonic log along the well ‎[3]. Finally, it can be calculated from the model of drilling, where utilizing data of drilling such as weight on bit, rotary speed and other drilling parameters for finding the mechanical properties of the rock. These drilling parameters can be obtained through the drilling process of the well for each foot ‎[4]. The main objective of this study is to calculate the value of the strength of the rock from the sonic log model where this value is called the unconfined compressive strength. After that, the study used value of unconfined compressive strength to calculate confined compressive strength for each well by depends on pore and hydrostatic pressure ‎[5]. 2- Calculation Unconfined Compressive Strength The use of sonic velocity log to calculate rock elastic properties are well established. Many correlations were presented between sonic travel time and rock strength or a grouping of different logs ‎[6], ‎[7]. Rock strength depends mainly on lithology. The rock strength was high for the rocks with low porosity or low traveling time. The equation used in this study is show below ‎[4]. ( ( ) ) (1) Where: Δtc : time of traveling. S0S : Rcock strength in case (UCS) k1, k2 are constants K1 = 5.15*10-8 K2 = 23.87 https://doi.org/10.31699/IJCPE.2019.1.7 K. H. Hassan and H. A. H. Abdul Hussien / Iraqi Journal of Chemical and Petroleum Engineering 20,1 (2019) 49 – 52 05 3- Calculating Confined Compressive Strength of Rock Unconfined compressive rock strength (UCS) that calculated from sonic log do not use in the apply model so should calculate the confined compressive rock strength (CCS) from (UCS) for any well or formations in the same field when we want to use the rate of penetration model. Confined compressive strength (CCS) calculation depends on hydrostatic and pore pressure because the drilling model use confined rock strength and the value of rock strength, which got from sonic model do not contain on the effect of the difference between hydrostatic pressure and pore. Rock strength is the chief element of the drilling models ‎[8]. ( ) (2) S: (CCS) in MPa, So: (UCS) in MPa, Pe different between pore and hydrostatic pressure. (as,bs) are fitting constants showing in Table 1. Table 1. Chip Hold-down Permeability Coefficients ‎[9] Formation Permeable Impermeable Pe Ph-Pp Ph ac 0.00497 0.0141 bc 0.757 0.470 cc 0.103 0.569 as 0.0133 0.00432 bs 0.577 0.782 4- Results The results of this work are presented for two wells (BU-47); (Bu-50) wells. The results are listed in the following figures (1 to 5) studies formation. These formations include Mishrif, Sadia, Middle lower Kirkuk, upper Kirkuk, and Jaddalla formations. Fig. 1. Comparison the values of UCS and CCS between (BU-50) and (Bu-47) wells for Mishrif formation Fig. 2. Comparison the values of UCS and CCS between (BU-50) and (Bu-47) wells for Sadia formation Fig. 3. Comparison the values of UCS and CCS between (BU-50) and (Bu-47) wells for Middle lower Kirkuk formation Fig. 4. Comparison the values of UCS and CCS between (BU-50) and (Bu-47) wells for Upper Kirkuk formation K. H. Hassan and H. A. H. Abdul Hussien / Iraqi Journal of Chemical and Petroleum Engineering 20,1 (2019) 49 – 52 05 Fig. 5. Comparison the values of UCS and CCS between (BU-50) and (Bu-47) wells for Jaddala formation 5- Discussion Figures (1 to 5) represent the comparison between (BU-50), (BU-47) for the unconfined compressive rock strength that is calculated from the measuring sonic log with confined compressive rock strength which calculated from UCS with depth. The difference between confined rock strength and unconfined rock strength depend on the value of hydrostatic and pore pressure. When the value of the difference between pore and hydrostatic pressure is very high that led to increasing differences between unconfined and confined compressive strength for each formation. It can be noticed that there is an only slight difference between the values of unconfined and confined compressive rock strength in upper Kirkuk formation. Mishrif, Sadia Middle lower Kirkuk has a high difference between unconfined confined compressive rock strength because there is a high difference between the hydrostatic and the pore pressure. The values of rock strength changed with depth, because of varying in the lithology with depth. In addition, it can be noticed the value of rock strength increases with depth. This increase in depth led to rising the rock strength. The rock strength in mishrif formation was higher than all formations because it is the deeper formation. The value of match for unconfined compressive strength between (BU-50) and (BU-47) for five formations (Mishrif, Sadia, middle lower Kirkuk, upper Kirkuk and Jaddala) was (97%, 87%, 96.5%, 97%, 86%) respectively. 6- Conclusions The values of unconfined compressive rock strength that obtain from (BU-50) well using sonic log tool have a very good match with the value of unconfined compressive rock strength which determined from (BU- 47) well for all formations. In addition, the difference between the values of confined and unconfined depends on the value of hydrostatic pressure for the same formation in two wells. The value of unconfined compressive rock strength mainly rose with increasing depth. Nomenclatures Symbol Definition ac chip hold-down coefficient, dimensionless ad drag-bit lithology coefficient, dimensionless as rock-strength lithology coefficient, dimensionless be chip hold-down coefficient, dimensionless bd drag-bit lithology coefficient, dimensionless bs rock-strength lithology coefficient, dimensionless cc chip hold-down coefficient, dimensionless Pe effective differential or confining pressure, psi Ph mud column hydrostatic pressure, psi Pp pore pressure, psi S confined rock strength, psi So unconfined rock strength, psi References [1] E. E. Okpo, A. Dosunmu, B. S. Odagme, and P. Harcourt, “Artificial Neural Network Model for Predicting Wellbore Instability,” no. August, pp. 2–4, 2016. [2] A. Asadi, “Application of Artificial Neural Networks in Prediction of Uniaxial Compressive Strength of Rocks Using Well Logs and Drilling Data,” Procedia Eng., vol. 191, pp. 279–286, 2017. [3] R. Between, F. Strength, D. Strength, and E. L. Properties, “SPE 18166 Relationships Between Formation Strength, Drilling Strength, and Electric Log Properties,” 1988. [4] P. B. Kerkar, S. I. E, G. Hareland, and E. R. Fonseca, “IPTC 17447 Estimation of Rock Compressive Strength Using Downhole Weight-on-Bit and Drilling Models,” 2014. [5] Hareland, Geir, and Runar Nygaard, “Calculating unconfined rock strength from drilling data, ” 1st Canada- US Rock Mechanics Symposium. American Rock Mechanics Association, 2007. [6] Tokle, K., P. Horsrud, and R. K. Bratli, “Predicting uniaxial compressive strength from log parameters, ” SPE Annual Technical Conference and Exhibition. Society of Petroleum Engineers, 1986. [7] Kazi, Asadullah, Zekai Sen, and Bahaa-Eldin H. Sadagah, “Relationship between sonic pulse velocity and uniaxial compressive strength of rocks, ” The 24th US Symposium on Rock Mechanics (USRMS). American Rock Mechanics Association, 1983. [8] M. Rastegar, G. Hareland, R. Nygaard, and A. Bashari, “Optimization of Multiple Bit Runs Based on ROP Models and Cost Equation: A New Methodology Applied for One of the Persian Gulf Carbonate Fields,” Proc. IADC/SPE Asia Pacific Drill. Technol. Conf. Exhib., 2008. [9] P. R. Rampersad, G. Hareland, and P. 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H. Hassan and H. A. H. Abdul Hussien / Iraqi Journal of Chemical and Petroleum Engineering 20,1 (2019) 49 – 52 05 تقدير مقاومة الصخرة من التسجيل الصوتي لحقل البزركان النفطي :دراسة مقارنة الخالصة تستخدم من الصعب جدًا الحصول عمى قيمة قوة الصخور عمى طول حفرة البئر. قيمة قوة الصخور التي إلجراء أنواع مختمفة من التحميل عمى سبيل المثال منع فشل جدار البئر ، وتحديد تصميم االكمال ، والتحكم في إنتاج الرمال. في هذه الدراسة يتم استخدام بيانات التسجيل الصوتي لحقل البزركان النفطي ، وطبقت هذه ، حساب قيمة قوة الضخرة بدون تاثير ضغط عمود ( . أوالBU-47)( )BU-50التالية الدراسة عمى االبار ( لكل تكوين من التسجيالت الصوتية اثناء الحفر . ان UCSالطين و ضغط التكوينات والتي يطمق عميها ب ) نتائج قوة الصخرة التي يتم الحصول عميها بتطبيق نموذج التسجل الصوتي ال تحتوي عمى تاثير ضغط عمود كوين وال يمكن استخدامها في تطبيق معادالت نماذج االختراق لذلك يتم حساب قوة ل وكذلك ضغط التئالسا باالعتماد عمى ضغط التكوين وضغط عمود السائل اثناء الحفر . ولمتاكد UCS)من قيمة ) (CCS)الصخرة ة بين قوة الصخرة لبئرين ومعرفة مدى التطابق بينهما .نمن نتائج قوة الصخرة تم المقار بناءا عمى النتائج التي تم الحصول عميها ، هناك تطابق جيد بين قيم قوة الصخرة التي تم حسابها من باالعتماد عمى التسجيالت الصوتية. حيث ان قيمة تطابق النتائج بين قوة (BU_50), (BU-47)االبار Mishrif, Sadia, Middle lower Kirkuk, upper Kirkuk, Jaddalالصخور لخمس تكوينات والتي هي عمى التوالي )٪.7٪، 58٪، 9..5٪ ، 78٪ ، 97 (كانت