More Ultradeepwater Drilling Problems

Abstract

A 1999 SPE/IADC paper (52782) identified and documented solutions to a number of drilling problems encountered in Ultra-deepwater drilling. Since that time the industry has pushed the water depth record beyond 10,000' of water and drilling depths below 32,000'. A number of new problems have occurred in the last 8 years that have been caused by mechanical failures (equipment stressed to its limits) or human error. In the Gulf of Mexico recent drilling has encountered problems drilling salt and tar that the industry had not previously experienced. Three operators active in deepwater GOM have collaborated on this paper to document problems under the assumption that understanding what can go wrong is the best way to avoid problems. Introduction In 1999 the water depth drilling record was 7,520'. There were 56 rigs advertised as being capable of drilling in greater than 5,000' of water1. The water depth record is now 10,011' 2 and there are 74 rigs capable of drilling in greater than 5,000' of water3. In the 1990s there were 148 wells drilled in the Gulf of Mexico in greater than 4,000' of water. By the 2000s (mid 2006) there have been 524 wells drilled in greater than 4,000' of water. The authors' companies have drilled 291 of these wells in the Gulf of Mexico since 2000. The number of wells being drilled in deepwater has increased. The water depth, total depth and complexity of those wells drilled in deepwater GOM has also increased. The depth record is now 34,189' MD4.

Wellbore Stability Problems in Deepwater Gas Wells

“…Over 75% of drilled deepwater formations are shale formations and drilling cost attributed to shale instability problems is extremely high. The causes of shale instability are mechanical instability and chemically induced instability as a result of interaction between mineral compositions of the formation and drilling fluid [17].…”

“…The factors that contribute to this wellbore problem are capillary pressure, osmotic pressure, pressure diffusion in the vicinity of the wellbore and wellbore fluid invasion during overbalanced drilling [17] [18]. During drilling, the drilling mud in the wellbore contacts the formation fluid through the pore-throat interface and as a result, capillary pressure is formed.…”

“…For a homogeneous formation layer, Darcy's law can be used to estimate the pore pressure distribution as shown in Equation (17). Where e p is the formation pressure at the external boundary of the reservoir, e r and w r are the radii of the external and wellbore wall respectively from the axis of the wellbore, and the value of r depends on the wellbore radius.…”

Study of Continuous Rheological Measurements in Drilling Fluids

“…This window represents the minimum and maximum pressures that can be applied to the system so as to avoid undesired flows towards the well, such as water or gas invasion originating from the rocks. The minimum pressure is known as porous pressure and the maximum is known as fracture pressure (Shaughnessy et al, 2007). To maintain the hydraulic pressure within the limits of the porous and fracture pressures, a common technique is the overbalanced technique.…”

Numerical Simulation on Deepwater Drilling Wellbore Temperature and Pressure Distribution

“…There are huge oil and gas resources in deepwater, but China is still in the initial stage for the deepwater drilling, facing many challenges. Deepwater low temperature, gas hydrates, shallow gas and shallow water flow, narrow mud density window, cuttings transport in large diameter riser segment, large amount of mud requirement, etc., make deepwater drilling even more challenging (Rocha et al, 2003;Shaughnessy et al, 2007;Close et al, 2008). Wellbore temperature and pressure prediction and control are critical techniques in deepwater drilling.…”