Managed Pressure Drilling Techniques

CHAPTER 1
INTRODUCTION
Managed Pressure Drilling (MPD) is a new technology that uses tools similar to those of underbalanced drilling to better control pressure variations while drilling a well [4]. The aim of MPD is to balance the downhole pressure and manage the annular hydraulic pressure accordingly in order to improve the drillability of a well by mitigating the drilling problems, including stuck pipe, lost circulation and excessive mud cost.
MPD can improve economics for any well being drilled by reducing a rig’s nonproductive time (NPT). NPT is the time that a rig is not drilling [4]. Many of the drilling problems may be reduced by using MPD as such problems occurred. MPD introduces new techniques that require proper understanding of the drilling problems, becoming confident enough in the technology to use it on a regular basis takes time. With the resources that are currently uneconomical in the offshore markets and the problems that occur while drilling a well, it is important that industries look to MPD to improve the drilling ability of the drilling rigs.

1.1 Background
The MPD is an adaptive drilling process to precisely control the annular pressure profile throughout the well [1]. The main idea is to balance the bottom hole pressure and maintain within close tolerances and close to the boundary of the operation envelope defined by the pore pressure, hole stability envelope and fracture pressure. MPD uses many tools to mitigate the risks and costs associated with drilling wells by controlling the annular pressure profile. These techniques include controlling backpressure, fluid density, fluid rheology, annular fluid level, circulating friction and hole geometry in any combination.

1.2 Problem Statement
The economics of drilling offshore wells is important as we drill more wells in deeper water, horizontal and high pressure high temperature (HPHT) wells. Drilling-related problems, including stuck pipe, lost circulation and excessive mud cost show the need for better drilling technology. If we can solve these problems, the economics of drilling the wells will improve, thus enabling the industry to drill wells that were previously uneconomical.

1.3 Objectives
The objectives of this project are:
a. To establish that the MPD techniques can be used to balance the downhole pressure environment limits and manage annular hydraulic pressure profile accordingly.
b. To develop a design for MPD techniques successful application.

1.4 Scope of Study
To achieve the objectives of this project, the scope of study are:
a. To conduct in-depth research on the drilling offshore wells and its pressure variation.
b. To conduct in-depth research on the case study of the well control equipments during the drilling operation
c. To conduct the analysis and design on the MPD techniques to mitigate the drilling related problems.


CHAPTER 2
LITERATURE REVIEW
Generally, the drill string connection procedure mainly consists of five operation, the rotational drill string stopped, pumping of drill fluid stopped, new segment of drill string is mounted to the drilling string, pumping drilling fluid restarted and drill string is rotated and the normal drilling operation is restarted[5]. The starting and stopping of the drilling fluid caused severe fluctuation in the well fluids flow rate which influences the well pressure. With the use of the MPD techniques will reduce this doubt by adding the surface pressure that controlled from the surface so that the bottom pressure will be the summation of hydrostatic pressure, Frictional pressure and surface pressure.
Managed Pressure Drilling (MPD) allows us to manipulate the pressure in the borehole whilst drilling and this allows us to eliminate pressure related issues, increasing Rates of Penetration (ROP) and increase control of the well. During the manipulation of the pressure in the well, the following variables normally manipulated. The mud density, mud viscosity, flow rate, trapped pressure and friction pressure.

2.1 Underbalance Drilling (UBD) Vs. Managed Pressure Drilling (MPD)
MPD is similar to Underbalance Drilling (UBD), it uses many of the same tools and were designed for UBD operations. The difference between these two techniques is that the UBD is used to prevent damage to the reservoir during the drilling whereas the MPD is to solve the drilling problems. The UBD allows influx of formation fluids by drilling with the pressure of the fluid in the wellbore lower than pressure and the fracture pressure of the reservoir. It is set up to handle the influx of fluids that may occur while drilling but does not encourage influx. UBD is reservoir-issue related while MPD is drilling-issue related [4].


2.2 Pressure-Gradient Window
As the well is drilled, drilling fluid is circulated in the hole to obtain a specific bottom hole pressure. The density of the fluid is determined by the formation and pore pressure gradients and wellbore stability [2].
Figure 2.1 shows a pressure gradient profile of a well. This profile shows the change in pressure as the depth increases. The pressure window is the area between the pore pressure and the fracture pressure. The aim when drilling a well is to keep the pressure inside this pressure window. In a static well, the drilling, the only way to adjust the pressure during static conditions is to vary mud weight in the well.

Figure 2.1 Pressure-gradient profile [4]
Figure 2.2 shows the problem that can occur when dealing with tight pressure gradient windows. When the well is static, the pressure in the well is less than the pore pressure and the well takes a kick; that is, hydrocarbons flow into the well. Before drilling can begin again, the kick has to be circulated out. After a connection, the pumps restart, the BHP (Bottom Hole Pressure) increases, and the pressure goes above the fracture-pressure, resulting in lost circulation, or fluid flowing into the formation. The goal of MPD is to walk the line of the pressure gradients. Managing the pressure and remaining inside this pressure gradient window can avoid many drilling problems.


Figure 2.2 Pressure-gradient window for tight margins [4]

2.3 MPD Techniques
2.3.1 Constant Bottom Hole Pressure (CBHP)
The CBHP will equalize the bottom hole pressure during the drill pipe connection due the lost of friction pressure when the pump at the surface is stopped and the circulation fluid into the well is stopped [1].

2.3.2 Pressurized Mud Cap Drilling (PMCD)
The PMCD permits safe and efficient drilling in severe or total loss zones so that there will no return flow by pumping the viscous fluid or disposable fluid (water) through the drill pipe [1].
2.3.3. Dual Gradient (DG)
The DG is aimed to recover the expensive with zero discharge. In DG drilling the bottom hole pressure is maintained via combination of two fluid gradients [1].



CHAPTER 3
METHODOLOGY
3.1 The Methodology of Study
















Figure 3.1 Flowchart of the methodology research


CHAPTER 4
Result AND DISCUSSION
4.1 Result
This report will come up with the analysis and design of the MPD techniques i.e. Constant Bottom Hole Pressure (CBHP), Pressurized Mud Cap Drilling (PMCD) and Dual Gradient (DG).

4.2 Discussion
With the MPD technology it will reduce the NPT which minimize the rig cost. The drilling problems such as Kick and lost of circulation will be mitigated using MPD techniques.

CHAPTER 5
CONCLUSION AND RECOMMENDATION
5.1 Conclusion
MPD can solve many of the NPT problems that occur while drilling offshore. By solving these problems, MPD can improve the economics of the drilling wells and enable the drilling of wells that previously were taught to be uneconomical.

5.2 Recommendation
In applying MPD in the field, many variations are still being developed. Using compressible fluids with MPD is an interesting variation that would allow drilling with a balanced pressure using air, foam or mist. This could result in increasing ROP when drilling while still keeping the pressure inside the gradient window. Another variation is having the ability to strengthen the wellbore using solids in the mud to plug and support microfractures that form in weaker formations when using a higher density mud. This variation would not be adjusting the pressure gradient of the wellbore but would widen the window so that the well could be drilled successfully.

REFERENCES
[1] N. Steve, May 2009, Managed Pressure Drilling, Weatherford Solution Sdn.Bhd, Kuala Lumpur
[2] F.John,Dr., Drilling Engineering, Heriot Watt Institute of Petroleum Engineering, Edinburgh, Scotland
[3] H. M. Don, 2007, Controlled Pressure Drilling, Weatherford International Ltd, Texas, USA.
[4] M. D. Matthew. May 2006, Managed Pressure Drilling, Texas A & M University, USA
[5] N. Gerhard & N. Geir, Journal of process control 16 January 2006, Nonlinear model predictive control scheme for stabilizing annulus pressure during oil well drilling, Department of Electrical Engineering Technology and Cybernetics, Telemark University College, Kjǿlnes Ring 56, N-3901 Porgrunn, Norway
[6] L.C. William, Ph.D, Air and gas drilling manual, New Mexico Institute and Technology, Secoro, New Mexico