Parameters optimization of oil well drilling operation

In the beginning of 2005, the ministry of natural resources in the Kurdistan region of Iraq divided its territory into more than 50 oil blocks based on geological setting. These oil blocks were awarded later to different international oil companies for oil investments based on Production Sharing Contracts (PSCs). A new oil-exporting pipe was also established from the region to the Jaihan port in Turkey at the Mediterranean Sea. This study is related to the oil well drilling operations in one of these oil blocks in northern Iraq which is referred as the Bazian oil block. Drilling operations in the nearby oil blocks (Taq Taq and Miran) were started earlier and the drilling data of those oil blocks were used as offset data in the drilling program of the Bazian block. High similarities were expected between these oil blocks with respect to lithology of the formations, oil well drilling techniques, and operation problems. By 2009 over twenty oil wells were drilled in the Taq Taq oil block and it is becoming one of the most important oil fields in the Kurdistan region. In the Miran oil block, exploration for oil and gas started in early 2008, and three oil wells were completed and started to produce crude oil. By the end of 2009, the geological and geophysical surveys in Bazian block were finished and the drilling operation started on October 1st the same year. This study (Parameter Optimization in Oil Well Drilling Operation) was recommended and sponsored by the Kurdistan Regional Governorate (KRG) aiming towards more optimized drilling in the future in the same oil block. Parameters like weight on bit, string rotation and rate of penetration for the future drilling operation in the Bazian oil block with more optimized values were predicted. This study was started by collecting detailed operational data from different sources during the operations of drilling the Bazian well Bn-1. Among many sources of data, Mud Logging Unit (MLU) data were selected for this study, as it was the most complete data set from the surface to the final drilled depth. This thesis contains the work of five published papers in the evaluation of the drilling operation at different intervals for the key well. Parameters for achieving the optimal penetration 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 highly fractured 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 effects were studied. Optimum drilling fluid, drilling technique, and drilling parameters were proposed for the future drilling operation. In the second paper (Kicks Controlling Techniques Efficiency in Term of Time) recorded data were analyzed to manage the drilling operation during the critical times in terms of controlling the Bottom Hole Pressure (BHP). Productive and none productive times were analyzed through the study of the drilling and tripping operations. Change in the drilling technique was proposed by modifying the drilling fluid. Drilling fluid as a first barrier to control formation pressure and well kicks were studied for their rheological properties. During the drilling operations two techniques, circulating techniques and non-circulating methods, were implemented to control the BHP. Both methods have been implemented to control kicks in the Bn-1 oil well and wells in other oil blocks in the region. The process of drilling design and casing setting points have been studied based on the utilization of accurate values of formation pressure. Data of formation pressures were used to design safe mud weights to overcome and prevent well kicks. The emphasis has been placed on the practical utilization of the kicks pressure near the reservoir. The presented relationships help in better understanding of the lithological columns and reduce possible hole problems during the kick appearance. Optimum casing setting point of the intermediate section was proposed for future operations. The third paper (Time Optimizing near the Pay Zone) was on the drilling operation inside the cap rock. Time managing was studied for surface preparation facilities, subsurface expected pressure control time, and the best technique to control the Bottom Hole Pressure (BHP). Well controlling techniques in oil and gas drilling operations are used to control BHP and avoid any fluid influx from formation to the well. Time consumed to control the formation pressure will range between a few hours to many days. This paper also discussed the hydrostatic pressure distribution and changes near the pay zone for the Bazian (Bn-1) oil well. Increasing linearly drilling fluid properties such as density and viscosity with time will help the engineer to better interpret sampling of the lithological columns and 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 drilled shale formations, the Tanjero and Shiranish formations. Wiper trips were evaluated based on the lifting capacity of the cutting in the drilling fluid. This paper discussed the wiper trip effects on well instability in shale formations. The problematic shale interval sections were studied with respect to the time spent on the wiper trip operations. Lifting efficiency and well wall instability are continuously changing with time. Detailed drilling operation, formation heterogeneity, rheological and filtration characteristics of the proposed polymer water-based mud were discussed. The physical and 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 in the annular. The relation between the net rising velocity and wiper trips were analyzed with support of results from laboratory works. Strong relationships were found between the wiper trip effects and lithology types of the penetrated shale. A modified drilling program was proposed in relationship to the casing setting point and drilling fluid properties that make the operations more optimized. The fifth paper (Controllable drilling parameter optimization for roller cone and polycrystalline diamond 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 Young model (BYM) for roller cone bits were used in the optimization process. This model describes the effect of eight parameters in one mathematical equation. The BYM was adjusted to be applicable for other types of drilling bits like polycrystalline diamond compacts (PDC) bits. Controllable parameters 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 lithological intervals were used to eliminate the effect of noisy data and to overcome the lithology homogeneity assumption used in other previous studies. A simpler model were introduced instead to optimize the string rotation. Multiple regression techniques were used in each cluster to determine optimized controllable drilling parameters. Optimized ROP, WOB, and RPM were predicted for future drilling operations. A clear relationship was found between the formation lithology and the controllable parameters in each cluster