Constructing a critical well is an exercise fraught with myriad details. The question that keeps responsible managers up at night is, “Did we forget anything?” Working the organization by tapping the experience of a multidisciplinary asset team provides benefits, but they are somewhat offset by the committee factor. The need for close collaboration establishes an equally important need for clear communications to achieve a successful outcome.

Anadarko Canada recognized the need for thorough planning when designing a drilling

Figure 1. An end-to-end workflow characterized well planning in the Petrel environment. (Images courtesy of Schlumberger)
program in the problematic foothills region of western Alberta. Each stakeholder played a critical role in the well’s success, yet achieving effective collaboration at all levels was tough. The company suspected that a significant reduction in drilling costs could be obtained simply by building an integrated workflow to guide the planning process to its logical conclusion. The workflow required that three different disciplines work together seamlessly: petrophysicists, geoscientists and drilling engineers. Furthermore, to achieve optimum efficiency, the contribution of the stakeholders needed to be integrated — it was unacceptable for them to work on the project sequentially.

In western Canada, drilling costs have increased by an order of magnitude over the last decade. But just attacking costs without a consistent plan is a recipe for disaster. The
Figure 2. Pore and fracture pressure gradient results in the pilot well show how the system would have predicted dangerous overpressured zones and allowed timely remediation to improve drilling efficiency and save money.
danger in cost-cutting drives is overlooking critical elements that ultimately produce the opposite effect. Accordingly, dual objectives were set — reduce costs while maximizing production. This simple goal changed the frame of reference from blind cost-cutting to achieving maximum profitability. The company turned to Schlumberger to help design a system that would ensure all critical factors were considered, including costs and risks, using intuitive, automated workflows that provided high efficiency (Figure 1). The system needed to be scalable so it could be used as effectively to plan a single well, a group of wells or an entire field.

A significant challenge
To get started it would be necessary to build a petrophysical and geological model of the field using all available data. This required that the system be designed to quickly accept a
Figure 3. Detailed 3-D structural models facilitate collaboration between geoscientists and drilling engineers and help them select optimum drilling scenarios that target reservoir “sweet spots.”
wide variety of input data, collate it and normalize it. One of the important features of the workflow should be its ability to take input from any WITSML-enabled server. This would allow the operator to use datasets from most service providers to plan wells. Within the model, which also should incorporate seismic data, the geologist must be able to pick the target and surface location and iteratively select the best trajectory assisted by expertise supplied by the drilling engineer. In close collaboration, the geologist and drilling engineer must be able to compare each proposed scenario in the context of risk, time and cost. The program must allow the team to reach the optimum decision efficiently using a consistent, standardized process, while considering all risks and contingencies so costs can be accurately estimated. From these requirements, the workflow was crafted.

Before testing the system on a real well, a pilot study was conducted on a previously drilled offset well. Using pre-drill data from the well project file, the team applied the new workflow to see what risks were predicted and if their exposure could be quantified in terms of costs and time. The results were validated using actual drilling data (Figure 2). The program’s ability to predict and quantify problems was cross-checked against actual problems encountered. The result confirmed the value of using the workflow — estimated at US $2 million in cost savings.

Encouraged by the results of the pilot program, the team applied the new workflow to its next critical well planning problem.

Built on experience
Based on Petrel seismic-to-simulation software, the system is augmented by modules that enable close interactive collaboration between members of the well planning team. The main
Figure 4. Within the 3-D Petrel shared earth model, well log suites can be synthesized in prospective wells before they are drilled. This helps geoscientists visualize target zones and anticipate log response when they are drilled.
system used included Petrel and Interactive Petrophysics applications to create a
3-dimensional shared earth model. The Osprey Risk Plug-in for Petrel enabled drilling engineers to quickly focus on achieving the best balance of risk, efficiency and cost. Using the plug-in, they could create a detailed operation program using a consistent and standardized approach. Finally, the Merak Peep application can be used to perform detailed analyses of project economics using deterministic or stochastic methods.

The essence of the Petrel application is the creation of a logical workflow that helps members of the multidisciplinary asset team make decisions that benefit other team members in achieving their objectives. The addition of the Osprey Risk plug-in streamlines the planning process by eliminating consideration of risky or inappropriate procedures. Use of the collaborative planning tool ultimately improves the drilling success rate while reducing non-productive time (NPT).

The collaborative nature of this workflow allows drilling engineers to be involved early in the planning cycle as part of the asset team. In this case, the drillers were brought in 6 months prior to the projected spud date. With the drillers’ early involvement, Anadarko experienced reduced time for the planning process while combining the ability to evaluate multiple scenarios quickly and with greater accuracy and confidence. The technology enabled the efficient and consistent creation of a thoroughly vetted well plan based on the integration of sound drilling engineering within the geological and geophysical environment.

The value is in the details
The interactive petrophysics application allows rapid calculation of key parameters that affect drilling efficiency and risk. Overburden pressures as well as pore and fracture pressure
Figure 5. Details of the analogous workflow are illustrated in this composite log/menu that allows access to all planning tools (left track) interactive parameter selection (center) and graphical representation of drilling parameters versus depth (right) together with risk factors.
gradients can be determined based on log data drilling information and seismic data. A comprehensive rock physics analysis is used to establish limits and identify potential problem areas. The system is very forgiving. For example, if density log data are unavailable, they can be quickly derived using sonic interval travel time. And seismic interval velocities can be used to project pseudo sonic data beyond the bit to identify dangerous geopressured zones before they are drilled. A number of commonly accepted practices can be used to model overburden, including a combination of density data, user-input average values, tabular data or empirical relationships. Pore pressures and fracture pressures and their corresponding gradients are similarly derived. Detailed petrophysical evaluations can be performed simultaneously to develop stratigraphic cross sections complete with porosity and hydrocarbon saturation information. These data are used to populate the Petrel
3-D earth model from which volumetric analyses can be performed to feed reserves calculations.

The Petrel model highlights the best-quality target zones within the reservoir and allows the geologist to pick the ideal landing spot and direction for the completion zone as well as the best surface location. With this information the geologist is ready to select the best wellbore trajectory in collaboration with the drilling engineer. Some of the tools available to facilitate communication between geoscientists and engineers are the structural model, a 3-D representation of the entire structure with layers that can be peeled off like an onion to expose the target strata and indicate where the highest quality reservoir zones are located (Figure 3). Special 3-D plots can be generated such as pore pressure volume to indicate potential problem zones, where unexpected influxes could occur or, conversely, lost circulation or drillstring sticking against a pressure-depleted zone. These help drillers visualize potential risks and pre-plan their mitigation or avoidance.

Another excellent planning tool is the ability to synthesize a well bore complete with log responses within the earth model (Figure 4). This attribute allowed planners to judiciously extrapolate data from the pilot well in context with all the parameters that defined the earth model to create a synthetic log suite in the proposed well before it was drilled.

Analysis of risks and their subsequent effect on costs and time are achieved using the Osprey Risk Plug-in. At its heart is an analogous workflow containing all the elements of well construction (Figure 5). Using this single workflow, the drilling engineer can collate all the data affecting the well plan. Tables of constants and variables, which can be used as-is or customized to fit regional norms, are easily accessible. All available input data, wellbore design information, drilling parameters and results are a mouse-click away. A graphic representation of the well plan contains risk factors plotted versus depth alongside pressure trends, drilling parameters, mud hydraulics and pump pressure for easy correlation.
Osprey Risk allows geoscientists to evaluate prospects using sound drilling engineering principles. It uses a common set of configuration files based on validated field best practices. Input is derived from the Petrel model ensuring a consistent, standardized approach. The output streams to all Osprey Risk reports whereby risk, time and cost effects can be quantified and prioritized. This workflow allows geoscientists to export their scenarios seamlessly to the drilling engineers, who can perform their economic evaluations considering risk/value tradeoffs to reach the optimum well plan.

Measure twice, cut once
This old carpenters’ axiom is an elegant way to describe the benefits of the collaborative well planning system. The ability to perform comprehensive planning using a logical engineering approach enabled the company to safely drill critical wells with utmost confidence. According to Anadarko, the well planning workflow brings drilling into the geoscientific collaborative environment, enabling fast, accurate evaluation of multiple scenarios. This permits iterative drilling engineering and well design beyond trajectory and interrelates time, cost and risk in a unique way using sound engineering principles. Andardarko saved time and money by completing 80% of their drilling workflow in 20% of the previous time. The repeatable, scalable and consistent process also saved the operator time and money by eliminating multiple spreadsheets and creating standardized reports in formats approved by the regulatory agencies.

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