Offshore United States, abandoned ERD wells are used as the mother bore to execute complex sidetracking operations to access satellite reserves.(Figure courtesy of Baker Hughes INTEQ)

Today’s drilling and completion technology allows operators to access and recover more hydrocarbons than ever before. An excellent illustration of this is the way in which both multilateral and extended-reach drilling (ERD) capabilities have advanced in recent years.

Not so long ago, due to technology and experience limitations, ERD wells were almost exclusively drilled with two-dimensional profiles — limiting the reservoir targets which could be accessed and leaving “inaccessible” reserves untapped. Today, it is possible to steer ERD wells in three dimensions at great depth to access otherwise stranded reserves. Using the latest technology and growing experience from related operations, these wells can also be drilled as multilaterals.

Why extended-reach drilling — or why not?

ERD wells are challenging, but the prize is huge. ERD wells allow access to otherwise stranded reserves, enable the use of existing surface infrastructure, and reduce environmental impact.

However, when planning an ERD application, the magnitude of the prize must be weighed against well construction costs and inherent operational risks. Even when baseline economics appear feasible, uncertainty associated with the inherent operational risks can result in ERD projects being cancelled. It is therefore crucial to thoroughly plan ERD projects to ensure the uncertainties associated with operational risks are understood, engineered out or minimized and, where necessary, have a priced contingency plan in place. As ERD experience grows and technology develops, risks and the uncertainty associated with those risks will decline. This improves the viability of an ever-increasing number of ERD programs and simultaneously pushes the ERD envelope. Evidence of this is seen in the fact that, in the past two years, long-standing (10+ years) ERD world records have been broken multiple times. However, not only has the ERD envelope’s magnitude been expanded, ERD well complexity has also increased. Today, some of the most geometrically complex wells which access difficult-to-get reserves are simultaneously highly extended-reach. Another indicator of this growing confidence is illustrated by increasing ERD activity in some of the worlds’ highest cost drilling environments (e.g., deepwater West Africa). Figure 1 shows an example of a complex ERD well drilled using existing offshore infrastructure to access satellite reserves.

With current and likely future market conditions, increased experience, knowledge transfer, and technology development, there is a growing justification to pursue ERD projects rather than cancel them.

Why multilateral — or why not?

As with ERD wells, there are a variety of benefits to constructing a multilateral well. These include:
• Exposing and producing from
additional reservoir;
• Drilling fewer wells;
• Extending well life;
• Delaying coning;
• Improving recovery;
• Reducing surface infrastructure; and
• Lowering environmental impact.

The types of reservoirs that can benefit from multilateral drainage programs can vary from thin or low-permeability reservoirs to those containing heavy oil reserves. Other reservoirs often considered for multilateral drilling include coalbed methane developments, shale gas basins, and reservoirs prone to coning.

In a similar manner to growth in ERD activity, multilateral developments are becoming increasingly common as benefits are accepted and experience, coupled with technology development, decreases operational risk. As a result, both the quantity and complexity of multilaterals are increasing. Figure 2 shows an example of a complex multilateral well drilled offshore Norway to drain oil from a thin sandstone reservoir.

Advances in automated directional drilling, such as INTEQ’s AutoTrak rotary steerable service, have been a key enabler to multilateral and ERD wells. Using rotary steerables, coupled with growing competence, multilateral well exits are reliably performed on depth and legs steered precisely within thin production zones. From a completions perspective, the introduction of self-aligning multilateral systems and drilling/reaming liner technologies, such as Baker Oil Tools’ Rotatable Self-Aligning RAM Multilateral and ControlSET Liner System in conjunction with Hughes Christenson’s EZCase and EZReam bits, have complemented the advances in drilling capabilities by enabling liners installed in sidetracks to get to required depth.

Multilateral ERD — coming soon?

Economics vary widely between different well types in different locations, but the percentage of total well construction cost of drilling an ERD well to top reservoir can account for 75% or more of the dry hole cost — often costing more than US $20 million just to get the well to top reservoir. Operationally, while constructing the well to top reservoir, many of the risks are encountered and passed. This includes achieving the required kickoff and build to high angle in large hole size, drilling and steering the high-angle tangent section to top reservoir, managing wellbore stability, and running and cementing the long string of casing/liner, etc. From an environmental perspective, it is common for more than 90% of the wells’ total drilled rock volume to be removed and disposed of safely by the time top reservoir is reached by an ERD well.

When planning an ERD well to a reservoir that will benefit from multilateral development, a question to ask is: Why not drill these ERD wells as multilaterals? There are many good reasons why this is not commonly done. These are primarily related to the increased challenge and operational risk added to an already challenging ERD well. The $20 million investment getting the well constructed to top reservoir is an investment worth protecting. The added risks of constructing an ERD well as a multilateral include:
• Setting and retrieving whipstocks at extreme measured depth;
• Sidetracking at extreme measured depth;
• Ability to rotate the multilateral system all the way to landing point;
• Increased torque and drag from the sidetrack, pushing the torque and drag past limits;
• Ability to complete the well to total depth (TD); and
• Considerations of added completion complexity at extreme measured depth.

However, as mentioned above, competency in delivering ever more challenging ERD and multilateral wells is increasing as technology matures, experience grows, and lessons learned are shared. Relevant experience in certain aspects of this type of operation is being gained. For example, on a recent ultra-ERD project in Eastern Russia, a casing whipstock was set and a sidetrack successfully performed at 25,883 ft (7,889 m) measured depth (MD). The sidetrack was then drilled to TD at 29,942 ft (9,126 m) MD in a single, trouble-free run. Another example of ERD wells being sidetracked successfully is offshore United States. Here, abandoned ERD wells are used as the mother bore to cost-effectively access satellite reserves. Figure 3 shows a sidetrack from one of these abandoned ERD wells. In this case, the sidetrack had to be drilled initially “uphill” before turning dramatically and dropping to intersect two targets aligned perpendicular to the original ERD well trajectory. A significant amount of planning was performed, which resulted in selection of specific technologies to mitigate identified risks. This included a one-trip whipstock exit system incorporating a polycrystalline diamond compact mill to minimize window exit time, reduce torque and drag, lower drillpipe fatigue, and facilitate liner running. Then, a rotary steerable system was used to provide precise steering, low tortuosity, and high drilling efficiency.

It is not uncommon to see multilateral legs reach to significant ERD proportions. In these examples, the well trajectory to top reservoir and individual leg exit points are not typically of “ERD proportions,” but the individual legs are extremely long and frequently drilled with highly complex trajectories to maximize reservoir coverage.

As experience is gained in these individual operations, lessons will be learned and combined to mitigate the risk of drilling ERD wells as multilaterals. It is therefore just a matter of time before we see true convergence of ERD and multilateral drilling techniques applied to more effectively develop those reservoirs that need it most.