Parameters optimization of oil well drilling operation

Abstract: In the beginning of 2005, the ministry of natural resources in the Kurdistan region of Iraq dividedits territory into more than 50 oil blocks based on geological setting. These oil blocks were awardedlater to different international oil companies for oil investments based on Production SharingContracts (PSCs). A new oil-exporting pipe was also established from the region to the Jaihan portin Turkey at the Mediterranean Sea.This study is related to the oil well drilling operations in one of these oil blocks in northern Iraqwhich is referred as the Bazian oil block. Drilling operations in the nearby oil blocks (Taq Taq andMiran) were started earlier and the drilling data of those oil blocks were used as offset data in thedrilling program of the Bazian block. High similarities were expected between these oil blocks withrespect to lithology of the formations, oil well drilling techniques, and operation problems. By 2009over twenty oil wells were drilled in the Taq Taq oil block and it is becoming one of the mostimportant oil fields in the Kurdistan region. In the Miran oil block, exploration for oil and gas startedin early 2008, and three oil wells were completed and started to produce crude oil. By the end of2009, the geological and geophysical surveys in Bazian block were finished and the drilling operationstarted on October 1st the same year.This study (Parameter Optimization in Oil Well Drilling Operation) was recommended andsponsored by the Kurdistan Regional Governorate (KRG) aiming towards more optimized drillingin the future in the same oil block. Parameters like weight on bit, string rotation and rate ofpenetration for the future drilling operation in the Bazian oil block with more optimized valueswere predicted. This study was started by collecting detailed operational data from different sourcesduring the operations of drilling the Bazian well Bn-1. Among many sources of data, Mud LoggingUnit (MLU) data were selected for this study, as it was the most complete data set from the surfaceto the final drilled depth. This thesis contains the work of five published papers in the evaluation ofthe drilling operation at different intervals for the key well. Parameters for achieving the optimalpenetration rate were predicted for the future operations.The first paper (Evaluation of Limestone Interval in the Drilled Surface Section of Bn-1 Oil Well)was on the evaluation of the drilling operation in the surface section from 9 m to 480 m. The highlyfractured Pila Spi formation was studied for its controllable parameters like Weight on Bit (WOB),drill string rotation (RPM) and the used torque. High loss of circulation and environmental effectswere studied. Optimum drilling fluid, drilling technique, and drilling parameters were proposed forthe future drilling operation.In the second paper (Kicks Controlling Techniques Efficiency in Term of Time) recorded data wereanalyzed to manage the drilling operation during the critical times in terms of controlling the BottomHole Pressure (BHP). Productive and none productive times were analyzed through the study ofthe drilling and tripping operations. Change in the drilling technique was proposed by modifyingthe drilling fluid. Drilling fluid as a first barrier to control formation pressure and well kicks werestudied for their rheological properties. During the drilling operations two techniques, circulatingtechniques and non-circulating methods, were implemented to control the BHP. Both methodshave been implemented to control kicks in the Bn-1 oil well and wells in other oil blocks in theregion. The process of drilling design and casing setting points have been studied based on theutilization of accurate values of formation pressure. Data of formation pressures were used to designsafe mud weights to overcome and prevent well kicks. The emphasis has been placed on the practicalutilization of the kicks pressure near the reservoir. The presented relationships help in betterunderstanding of the lithological columns and reduce possible hole problems during the kickappearance. Optimum casing setting point of the intermediate section was proposed for futureoperations.The third paper (Time Optimizing near the Pay Zone) was on the drilling operation inside the caprock. Time managing was studied for surface preparation facilities, subsurface expected pressurecontrol time, and the best technique to control the Bottom Hole Pressure (BHP). Well controllingtechniques in oil and gas drilling operations are used to control BHP and avoid any fluid influx fromformation to the well. Time consumed to control the formation pressure will range between a fewhours to many days. This paper also discussed the hydrostatic pressure distribution and changes nearthe pay zone for the Bazian (Bn-1) oil well. Increasing linearly drilling fluid properties such as densityand viscosity with time will help the engineer to better interpret sampling of the lithological columnsand reduce possible hole problems.Paper number four (Wiper Trips Effect on Wellbore Instability Using Net Rising Velocity Methods)was on the effect of wiper trips operations to control parameters during the operations in two drilledshale formations, the Tanjero and Shiranish formations. Wiper trips were evaluated based on thelifting capacity of the cutting in the drilling fluid. This paper discussed the wiper trip effects on wellinstability in shale formations. The problematic shale interval sections were studied with respect tothe time spent on the wiper trip operations. Lifting efficiency and well wall instability arecontinuously changing with time. Detailed drilling operation, formation heterogeneity, rheologicaland filtration characteristics of the proposed polymer water-based mud were discussed. The physicaland chemical properties of the drilled formation and drilling fluid were also studied.Wiper trips were analyzed based on recorded history in relationship with the controllable parameters.Two calculation models have been implemented to find the net rising cutting particle velocity inthe annular. The relation between the net rising velocity and wiper trips were analyzed with supportof results from laboratory works. Strong relationships were found between the wiper trip effects andlithology types of the penetrated shale. A modified drilling program was proposed in relationship tothe casing setting point and drilling fluid properties that make the operations more optimized.The fifth paper (Controllable drilling parameter optimization for roller cone and polycrystallinediamond bits) predicts optimized Rate of Penetration (ROP), WOB and the string rotation (RPM– rotation per minute) for the entire drilled well. The most used empirical Bourgoyne and Youngmodel (BYM) for roller cone bits were used in the optimization process. This model describes theeffect of eight parameters in one mathematical equation. The BYM was adjusted to be applicablefor other types of drilling bits like polycrystalline diamond compacts (PDC) bits. Controllableparameters like WOB, RPM and ROP were clustered based on changes in Bottom Hole Assembly(BHA) and lithology before running the model.The implemented clustering and averaging method for the collected data in short lithologicalintervals were used to eliminate the effect of noisy data and to overcome the lithology homogeneityassumption used in other previous studies. A simpler model were introduced instead to optimize thestring rotation.Multiple regression techniques were used in each cluster to determine optimized controllable drillingparameters. Optimized ROP, WOB, and RPM were predicted for future drilling operations. Aclear relationship was found between the formation lithology and the controllable parameters ineach cluster.