In an effort to continuously optimize drilling operations and economics, an operator examined the impact of adding hollow-glass spheres (HGS) directly to the drilling fluid formulation instead of performing underbalanced drilling operations. Both nitrogen and HGS were believed to reduce hydrostatic pressure of the mud column in the hole, resulting in higher drilling rates of penetration (ROP) and fewer mud losses to the wellbore.Invert emulsion fluid was blended with HGS on three drilling rigs using a specialized, environmentally acceptable mixing system to help reduce density. HGS concentration and fluid density were monitored and maintained while drilling over the period of one to three weeks for these three wells. The proper type of centrifuge and its setup is fundamental to maintaining low-gravity solids (LGS) at an acceptable level for proper fluid management while maintaining the desired concentration of HGS.Drilling mud density was reduced, as expected, and mud loss was minimized as a result. Overall costs were reduced because of less invert emulsion fluid loss, a reduction in the amount of lost-circulation material mixed compared to previous wells in the area, and less time spent on the drilling rig attributed to not having to stop to mix lost-circulation material or prepare new invert emulsion fluid volumes to replace losses. A significant ROP increase was not observed during this trial. The addition of HGS is a cost-effective solution to help reduce fluid loss in the Kakwa field of the Western Canadian Sedimentary basin. This trial helped reduce overall rig time, and fluid loss experienced was less than in previous wells in which this technology was not used.This paper provides information on HGS as an economic alternative to nitrogen to help reduce the hydrostatic pressure of invert emulsion drilling fluids using a small-footprint, environmentally acceptable mixing system.

Underbalanced drilling (UBD) has several advantages compared to conventional drilling. These advantages include the elimination of formation damage, higher penetration rate, reducing circulation loss and the possibility of actually producing hydrocarbons during the drilling process. UBD technology and applications have recently been applied while drilling challenging wells in Iranian fields. It is generally accepted that the success of underbalanced drilling is dependant on maintaining the wellbore pressure in an operational window determined by the formation pressure, wellbore stability, and the capacity of the surface equipment. There are several models which can predict the wellbore pressure. Traditional models are mostly empirical and lead to acceptable results for specific conditions but fail for other conditions. In the last decade of the last century, some mechanistic models have been developed which result in an acceptable range of outcomes for a wide variety of reservoirs. On the other hand due to the dynamic nature of the process, some researchers have recently focused on development of dynamic models. This paper presents an improved, comprehensive, mechanistic model for pressure prediction through a well during UBD operations. The comprehensive model consists of a set of correlations for predicting flow pattern and estimating the pressure in addition to two-phase flow parameters in bubble, dispersed bubble, and slug flow. On the other hand the most recently developed empirical correlations have been applied to determine PVT properties. The accuracy of these correlations has been tested in more than 20 oil wells in Iran. Naseri et al. and Almarhoun correlations was applied to determine the live and dead oil viscosities. Naseri et al. model which was originally developed for Iranian reservoirs was used in our model and the results are promising.

Seven Generations Energy Ltd. (7Gen) has drilled several horizontal wells in the extremely liquids rich Montney formation in the Karr Kakwa area of central western Alberta. Over the last two years we have seen progressively shorter drilling times as well as a marked increase in production as a function of optimal hydraulic fracturing recipes and completion installations. This paper will discuss the systematic approach taken by well construction engineers to optimize drilling performance through bit selection coupled with vibration mitigation and hydraulics optimization. Further technologies that will be discussed and will/have been be implemented are torque mitigation technologies to mitigate stick slip and the use of managed pressure drilling techniques to decrease mud density and further increase ROP’s. This paper will also discuss the coincident work done to optimize fracture treatments as a function of rock strength and measured gas response while drilling.

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Summary Computer simulation technology has been widely applied in many drilling engineering areas to simulate drilling engineering problems and optimization, to train engineers with real drilling operations and/or to handle rare applications and accidents. Among the increasingly applied drilling operations is under-balanced drilling (UBD). UBD is the drilling process in which the wellbore pressure is intentionally designed to be lower than the pressure of the formation being drilled. This results in a higher rate of penetration (ROP) and prevents fluid losses and related causes of formation damage. This paper presents the design and development of a UBD simulator, which is computer software that simulates and integrates the effects of: Bottomhole pressure (BHP). Minimum volumetric gas and liquid requirement. Required backpressure (BP) for required cutting removal to surface and controlling BHP. Kinematic energy per unit volume used in the hole cleaning considerations. Stand pipe pressure (SPP). Rock drillability. ROP. Drilling costs per metre. The goal of the simulator is to enable the user to pre-simulate different scenarios of the UBD drilling operations; therefore, the ideal optimized combination of drill bit durability and drilling efficiency, integrating all UBD operational parameters affecting the overall cost, can be obtained before the fact. The UBD simulator is designed to simulate most of the basic technologies of UBD (air, aerated and foam drilling). The goal of the UBD simulator is to design an effective UBD program by linking the BHP to rock drillability, which takes into account the effect and degree of under-balance on the effective rock strength, ROP and $/m that can be optimized for the operation. The complete UBD optimization integration is shown herein with illustrations including flowcharts.