Managed Pressure and Underbalanced Drilling - Coursework Example

Managed Pressure and Unbalanced Drilling in Oil and Gas Industry Oil and Gas are the backbone of modern technological economic and technological market. With the increase population and development of technology, energy consumption has increased. Therefore, the need of oil and gas extraction has also increased. This has resulted in the development of methods for efficient and convenient drilling mechanisms to overcome flaws in the conventional methods and to provide energy efficient methods. Modern oil and gas industry is exclusively based on managed pressure drilling and unbalanced drilling mechanisms. Both of these two methods have their own significance and are used based on a number of factors including area to be drilled, type of fuel to be extracted, geometry of the bore hole to be drilled and chemistry of the soil. This paper gives an insight into the basic drilling mechanisms and how they evolved to produce intelligent, cost effective and reliable systems. Keywords: Managed pressure drilling, Conventional drilling, underbalanced drilling. Introduction The economic revolution of modern era is exclusively based on the availability of quality oil and gas products. Therefore, scientists have been working on various methods to improve the extraction procedures for fuel. Underbalanced drilling and managed pressure drilling are two of the most common drilling techniques being implemented in today’s oil and gas industry. Underbalanced drilling is opposite to conventional drilling technique. In this technique wellbore pressure is kept lower as compared to formation fluid, this result in the smooth movement of formation fluids to the surface of the well bore(Gala and Toralde, 2011) and helps avoiding blow outs. Underbalanced drilling is good to be used in drilling rigs as it provides least wear to the well with increased production rate(NW_Air, 2014), but meanwhile, this technique is expensive and unreliable. While drilling deeper in the wellbore, it is sometimes difficult to maintain underbalanced condition and the pressure within the wellbore is increased may be as a result of increased density of soil. The boring will ultimately be shifted to overbalanced condition and this may harm the system resulting in irreversible damage and making the oil extraction expensive. Another most common drilling technique is the modification of overbalanced technique and is used where wellbore pressure is kept higher but is continuously monitored and maintained in order to avoid any unpleasant situation. If the wellbore pressure becomes excessively high, then it is maintained by making use of different densities mud and formation fluids and also controlling by not generating continuous influx formation fluid to the surface of wellbore. This method is exclusively known as managed pressure drilling as it makes used of an adaptive technique to control the balance between the wellbore and its environment(Montilva et al., 2010). Literature Review Underbalanced drilling is performed by making use of a number of drilling mediums. Some of the most common types of underbalanced drilling mechanisms being extensively used in oil and gas extraction are(Omni_Compressed_Air, 2014, Bennion et al., 1998): Air (Dust) Drilling Nitrogen Based Drilling Mist Drilling Aerated Fluid Drilling Percussion Hammer Drilling Payzone Drilling Air/gas based drilling mechanism is most commonly implemented in onshore and offshore oil and gas rigs(Midland, 2013). Research shows that gas based underbalanced drilling provides better pressure stability at the well bore by decreasing the density of drilling fluid and hence, providing least damage to the formation. In this type of drilling technique, gas like nitrogen is introduced into the well with a specialized tubing mechanism, capable of providing controlled pressure to the well bore, in order to maintain the underbalanced condition. Here is the pictorial view of typical underbalanced drilling mechanism as compared to a conventional one. Figure 1: Unbalanced Drilling vs Conventional Drilling If underbalanced conditions are not maintained then there is an increased risk of the well bore instability. In order to make sure that the underbalanced conditions prevail throughout the drilling process, factors impacting the dynamic pressure of the bore hole must be studied in detail. The bore hole pressure is expressed as(Wang et al., 1997): --------1 Where ph = hydrostatic pressure pf = frictional pressure loss component pacc= fluid acceleration pressure pwh= well head back pressure With the passage of time a number of modifications have been introduced to improve underbalanced drilling technique. Primitive method is to make use of jointed pipes for drilling but now coiled tubing is being commonly used in new installations. Coiled tubing has a number of benefits over conventional jointed pipe mechanism(Bennion et al., 1997). It helps in providing good housing for instrumentation unit which helps in continuously monitoring and controlling the pressure at the bore head. This design also helps in faster penetration and effective cleaning of the drilled hole but is expensive as compared to joint pipe mechanism. Another important drilling mechanism is managed pressure drilling which is most versatile and advanced drilling mechanism. It exclusively makes use of an adaptive control system and is capable of providing efficient extraction of oil and gas in least time, hence improves productivity(Landet et al., 2012). The fluid formation generated in managed pressure drilling is not taken to the surface of the bore continuously but is controlled by a choking valve which gets opened when the pressure equilibrium within the bore gets unstable(Strata, 2014); as a result, pressure at the bottom (bore) hole is kept constant. Below is the detailed view of a typical managed pressure drilling mechanism. Figure 2: Cross-Sectional View of Managed Pressure Drilling Mechanism Like other drilling techniques, managed pressure drilling was also having some limitations initially. These limitations included pipe cleaning issues, cost of mud and boring hole, lost circulation which effectively would result in increased percentage of non-productive time. These issues can be resolved by controlling frictional losses at the bore head especially in case of narrow drilling windows. This is done by introducing a pump at the bore head which pumps all the fluid to the surface of the hole and thus reduces the friction(Rohani, 2012). Another method of improving managed pressure drilling technique is to maintain density of the mud the boing head faces while drilling the hole. MPD system is designed in a way to keep the hydrostatic pressure of the mud in the well at a higher pressure as compared to the formation pressure(Elliott et al., 2011). This is done by developing a highly intelligent adaptive control system that is capable of maintaining the formation pressure to a constant lower level by the help of choke valve. As soon as the formation pressure starts increasing the system generates a signal and choke valve is get opened. Such a highly intelligent system can replace most of the labor requirements as well. Discussion and Conclusion Underbalanced drilling is used as it reduces the risk of damage of formation which may occur as a result of high production rate. This drilling technique is having high rate of penetration and as a result reduced time and cost of drilling is implied(Bennion et al., 1997). Also underbalanced drilling systems are efficient with least rate of mud choking and differential sticking which increase time of drilling. This drilling technique is also considered environment friendly as least mud pits are formed. Managed pressure drilling also provides all these features along with the feasibility of drilling the locations which are considered un-drillable for other conventional techniques(Maeland, 2013). This property makes managed pressure drilling most versatile method. If we compare underbalanced drilling with managed pressure drilling we notice almost similar trends in both the techniques but due to cost effectiveness and having good reliability standards, managed pressure drilling is preferred(Bergerot, 2011). Here is the graph showing the comparison of three drilling techniques(Gala and Toralde, 2011). Figure 3: Gaph showing drilling trends of various techniques Bore hole pressure for underbalanced drilling and managed pressure drilling can be determined by making use of the same expression given below. This expression measures pressure while drilling. ------2 Where, ECD= equivalent circulating density MW= mud weight When the bore head is static, pressure can be measured as: -------3 References BENNION, D. B., THOMAS, F. B., BIETZ, R. F. & JAMALUDDIN, A. K. M. 1997. Coil Tubing- The Future of Underbalanced Drilling? International Conference on Coiled Tubing Technologies. Dallas, Texas. BENNION, D. B., THOMAS, F. B., BIETZ, R. F. & JAMALUDDIN, A. K. M. 1998. Using Underbalanced Drilling to Reduce Invasive Formation Damage and Improve Well Productivity- An Update. Petroleum Society of CIM. BERGEROT, J. L. 2011. Managed Pressure Drilling with the ECD Reduction Tool. Annual Technical Conference and Exhibition Huston, Texas. ELLIOTT, D., MONTILVA, J., FRANCIS, P. & ROES, V. 2011. Managed Pressure Drilling Eases the Lines. Oilfield Review Spring. GALA, D. M. & TORALDE, J. S. 2011. Managed Pressure Drilling 101: Moving Beyond “It’s Always Been Done That Way”. The Way Ahead, 7. LANDET, I. S., PAVLOV, A., AAMO, O. M. & MAHDIANFAR, H. 2012. Control of Heave-Induced Pressure Fluctuations in Managed Pressure Drilling. American Control Conference. IEEE. MAELAND, M. 2013. Managed Pressure Drilling. MIDLAND. 2013. Ai Dilling Reduces Drilling and Servicing Costs and Increases Oil and Gas Production Rates. MONTILVA, J., FREDERICKS, P. & SEHASH, O. 2010. New Automated Control system Manages Pressure and Return FLow while Drilling and Cementing Casing in Depleted Onshore Field. IADC/SPE Drilling Conference and Exhibition. New Orleans. NW_AIR. 2014. Underbalanced Drilling. Available: http://nwairservices.100wd.net/services_underbalanced.php. OMNI_COMPRESSED_AIR. 2014. Underbalanced Drilling. Available: http://www.omnicompressedair.com/unbalanced-drilling. ROHANI, M. R. 2012. Managed- Pressure Drilling: Techniques and Options for Improing Opeational Safety and Efficiency. Journal of Petroleun and Coal. STRATA. 2014. Managed Pressure Drilling. Available: http://www.strataenergy.net/managed_pressure_drilling. WANG, Z., BIJLEVELD, A., MAGLIONE, R. & GAZANIOL, D. 1997. Underbalanced Drilling Requires Downhole Pressure Management. Oil and Gas Journal. Read More