With an estimated 50% of perforation clusters and 25% of stages not contributing to production from wells in all of the major shale plays, Schlumberger is focused on reducing the number of defective wells and improving completion quality.
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In looking at the Barnett, Marcellus, Haynesville and Fayetteville shale plays, most of the wells – perhaps 50% or more – produce less than 1.0 million cubic feet of gas per day in the first year. Today, with gas around $2.60 per million Btus, these wells would definitely be uneconomic, said Kyel Hodenfield, vice president, unconventional resources, Schlumberger.

“We are challenged to create technology that will apply and reduce that impact by improving on the defects we have in those wells if we can,” he told participants at the NAPE Business Conference on Feb. 22 in Houston. “Take the fact that there are a lot of defects in the well manufacturing process. We know we have to drill a lot of wells. We’re talking about 40,000 or 100,000 wells to fill in the Marcellus or Bakken.”

The industry is focusing on what can be done to reduce the impact of those defects, to drill more wells from a single pad, to reduce that pad from 10 to 5 acres, and even to reduce the number of truck trips.

“We would never have thought to put that in our plans five years ago, but today it is pervasive across everything from drilling to evaluation to completion,” he emphasized.

One aspect is completion quality. “We need to be able to fracture these rocks and maintain the conductivity in that fracture. And, the technology we apply to each of these basins is different because of the mineralogy and differences between them. For this, we’ve got a couple of work flows that we have developed that help both ourselves and our clients plow through these technological challenges to reduce the well defects, and the stage and perf cluster defects,” he explained.

For example, 3D geologic earth modeling helps identify sweet spots within a basin. “This is a multi-well scenario where we are looking at the 3D environment. A plug-in called Mandrill is a single-well, work flow that helps us optimize the completion and reduce the number of stages and perf clusters that do not contribute to production,” he continued.

“The advent of seismic combined with petroleum system modeling has been one of the things that has led to success. We are big proponents of basin modeling, which is simply recreating the depositional environment of that basin through time. We’re targeting where total organic compounds (TOC) or organic carbon may have accumulated, been preserved and buried to the proper depth to achieve that thermal maturity,” Hodenfield said.

Data collection is also crucial to cutting the number of defective wells. “Because of the dearth of date you have in these unconventional plays, you have to make use of every bit of data that you have and roll that back into a 3D earth model. Then you integrate it,” he noted.

“Seismic for conventional wells is used to look at structural boundaries and fluid contacts, such as oil, water and gas. On the unconventional side, it is gaining popularity, but from a different aspect.

“These are the most complex rocks I’ve seen across the world,” he emphasized. “What is productive or unproductive is very subtle in an unconventional well. Going from 7% to 8% gas-field porosity down to 4% might mean having a 2.0- to 5.0-million-cubic-feet-per-day well drop to nothing because it doesn’t produce.

“Changing clay content from 4% to 10% might mean going from a very productive field to something that can’t be fraced. Being able to discern those attributes with seismic is now becoming more prevalent,” he added.

Integrating data -- seismic, cores, cuttings, logs, drilling data and production data -- has been a part of the mantra in the industry over the last five years. “Anything that you can get to help you identify those sweet spots and eliminate those unproductive wells is important,” he stated.

The data is useful in determining what to target, where to place the pad, where to drill next and how many wells per pad. “There is a software application you can utilize that takes into account not only subsurface characteristics, but also the surface facilities so that you don’t plan a pad in the middle of the little town’s bank parking lot,” he said.

In terms of completion and reservoir quality, the vertical variability is also important given that many shale formations are 200- to 400-ft thick. Completion quality near the wellbore could be a choking point to production.

Identifying good completion quality or competent rocks from a vertical suite of logs is followed by simulations on fracturing sections. Once you know you can get some fracture width and maintain that width and conductivity, you can place that well, Hodenfield stated.

Once the well is planned and placed, the next step is optimization. “Today, many of the wells have geometric stages of perf clusters. Every 75 ft or so, we’re going to place clusters. However, there is information we can utilize to optimize that.

“There is a discrete fracture network that exists that we can measure. There is geomechanical data that we can also use to place the clusters,” he explained.

Sometimes it is favorable to have fractures. But, if you fire a perf cluster where you have multiple fractures, you will get fractures that compete for the fluid. “You’ll end up with two or three narrow fractures rather than one wide fracture next to the wellbore.

“Generally, you want to have stages where you are fracturing rock that is alike. But, because of lateral heterogeneity, you will end up crossing different reservoir characteristics that may be uneconomic. If you have reservoir quality but you don’t have permeability or gas saturation in place, you should avoid it,” he continued.

Schlumberger has devised a scheme called reservoir quality and completion quality. “Where you have a combination of these, you will place your best stages. It is very important to place the perf clusters within rocks with similar stresses. If you have perf clusters in dissimilar rock stresses, you will get perf clusters that do not contribute because these did not take that frac,” Hodenfield continued.

In a geometric completion with 17 stages, the clusters are arranged evenly through the stages. In the completion quality scheme, there are stages that do not have perf clusters and other areas where perf clusters are closer when placed in rocks with similar stresses.

“This is a very fast process. It can be done with logging while drilling, in cased-hole with new-age sonic tools or it will be done in the future in through-bit logging tools,” he noted.

Schlumberger’s Mangrove software has the ability to look at the microseismic data so that an operator can map whether there are bi-wing or complex fractures. Then, the operator can run simulations on the production. Before fracturing, the stages can be optimized.

“The technology is all aimed at reducing the number of defective wells, stages and perf clusters,” he emphasized.

Regarding reducing water usage and truck traffic, for example, Schlumberger has a commercial product called HiWay, which is channel fracturing.

“From calculations published by SPE, about 75% of the fluid pumped into a fracture never comes back. It is an ineffective use of that water. The fracture never gets propped or the fracture gets propped and never cleans up,” Hodenfield said. “Only about 25% of the fracture that is actually produced contributes to production.

Channel fracturing is a methodology that combines chemistry, fibers, proppant and a procedure that pulses the proppant in rather than having one continuous stream of proppant.

“What this does is provide a series of channels in that fracture and provides superconductivity back to the wellbore. In addition, it allows the proppant to get further out into the formation and be much more effective with the materials that you use.

“For production, we have run a number of jobs in eight countries – about 2,500. Production almost always over a series of wells is 30% to 50% higher. One of the big benefits is that we use about 40% less water and 30% less proppant. This reduces truck traffic by an order of magnitude,” he continued.

Hodenfield concluded his presentation by pointing out that Schlumberger is committed to full disclosure regarding everything the company pumps into wells. The company participates in Frac-Focus.

Contact the author, Scott Weeden, at sweeden@hartenergy.com.

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