Several factors can be adjusted in a hydraulic fracturing job
design to positively affect efficiency and cost. Using predictive analysis for
pressure estimation, with a focus on casing optimization, creates the potential
to accurately forecast timelines, reduce costs and maximize efficiencies with
minimal frac job design volatility.
CAMERON HORNOR, Universal Pressure Pumping
speaking with completion engineers about their priorities in planning and
executing a hydraulic fracturing job, efficiency and cost sit near the top of
their list. These aspects are so closely intertwined and co-dependent that one
cannot be manipulated without carefully considering the effect of the other.
When considering the frac job holistically, many factors can be tweaked to
maximize efficiency while also reducing costs. Two of these factors are pumping
rate and pressure.
and pressure are the foundation of a frac job. Drilling programs, casing
designs, frac horsepower needs and many other factors rely solely on rate and
pressure requirements for a well, with the objective that one can reach top
rate throughout the frac while remaining under the maximum allowable surface
pressure. Both rate and pressure are chosen in ways to enhance the efficiency
of the job and optimize stimulation in efforts to maximize the estimated
ultimate recovery of the well.
the challenge. So, what happens when one of these requirements
cannot be reached during the frac? In most cases, the shortfall comes in reduced
treatment rates, due to high treatment pressures. These diminished rates can
drastically affect the efficiency of the frac job, consequentially driving up
overall completion costs and delaying cash flow returns. With a high-performance
friction reducer already being used, and limited desire to make drastic changes
to the perforation or sand slurry design, options are limited to counter high
pressure and reduced treatment rates. If similar problems are predicted on
future wells, an adjustment in some aspect of the completion design must be
made early in the planning process.
approach. To help operators solve this issue, Universal
Pressure Pumping has developed a method for evaluating casing design
sensitivity, using a predictive pressure analysis tool. The internally
developed tool provides the ability to input planned pre-job parameters, such
as fluid type, perforation design and fracture gradients, which generate a
summary of the expected treatment.
of the most important outputs include tubing friction, maximum achievable rate
and pressure at maximum rate, all on a stage-by-stage basis. Knowing these
factors, the tech services team has the ability to present variations in casing
design that can positively affect the overall treatment and frac efficiency of
the well. By providing operators with an extensive breakdown differentiating
potential casing designs and the effects of those designs on their wells, they can
confidently choose a design that best aligns with their desired well treatment,
costs and efficiencies.
factors are considered when using the predictive pressure analysis tool. Most
inputs are design constants, including well lengths and depths, stage count and
treatment volumes. The tool though, also includes factors that have more
potential for variability like perforation design, estimated average
instantaneous shutdown pressure (ISDP), percent friction reduction and, of
course, casing design. These are the variables that are explored most by the technical
services team when looking at ways to maximize rate throughout a job.
few of these variable inputs are relatively easy to investigate and are identified
as “educated constants,” meaning that though they are not operator-provided
constants, like measured depth or stage count, they still could be accurately
estimated for the pressure analysis. These educated constants include
perforation design, average ISDP and percent friction reduction. Although modification
in perforation and cluster design influence rate and pressure, without a
drastic change, the alterations yield is negligible to overall treatment. Estimating
average ISDP is performed by gathering and analyzing completion data from
nearby wells in similar plays, and then predictions are made based on
water analysis utilizing water that will be used on the job and a variety of
friction reducers at the operator’s disposal provides an accurate friction
reduction percentage for the analysis. With the number of potential variable
factors now reduced to one, casing optimization can now be the focus. Casing
design changes provide the largest range in rate and pressure fluctuations from
the well. Many factors are taken into consideration when analyzing a casing
redesign for a more effective frac, including single string vs. tapered string,
casing size and casing weight.
1 illustrates a generalized example of the wide
range of maximum rates and pressures of a well, based on its casing design.
Some of the major sources of rate and pressure differences are tubing friction
and the maximum pressure rating of the casing. Changing casing size, or
introducing a tapered string to the design, has a significant effect on total
tubing friction throughout the system. Tubing friction has a direct correlation
to surface pressure, which in turn directly affects the achievable rate. Weight
of the casing used throughout the design also must be closely considered.
Increasing the casing weight of the weakest part of the string will up the
maximum pressure rating of the total design, in turn increasing the achievable rate
of the well.
can consider this comparative analysis and explore options, based on their
anticipated completion design, cost and casing availability. Casing design B
and C yield similar results in terms of rate and pressure analysis, but may
include a string of casing that is unavailable or uneconomical to purchase, Table
1. Through this analysis, an operator also may conclude that if they
increase casing size, they may be able to extend the length of well lateral,
due to reduction in friction pressure when compared with the original design.
These types of scenarios, and many others, must be taken into consideration by
the operator when designing their casing string. The predictive pressure analysis tool is particularly
useful here, because of the ability to quickly change inputs and rapidly sort
through the multitude of viable and nonviable options.
ease and accuracy of the predictive analysis tool recently led a Permian-based
operator to seek advice from the technical services team regarding pressure
analysis confirmation. Working in a sensitive formation, where operating at top
rate was key to optimizing fracture complexity, the customer wanted to confirm
that the current casing design would be able to withstand a 20% increase in
rate while allowing them to remain under the maximum pressure rating of the
well. Using current well parameters and pre-frac inputs, the team was able to
confirm that the well could, indeed, be fractured at optimum rates while staying
below maximum pressure restraints throughout the entire job.
1 represents a stage-by-stage analysis of the
actual job treatment, paralleled with the pre-frac predictive pressure analysis,
indicating the frac job held true to predictive analysis, and the job was
completed without any rate or pressure limitations. Not only was the operator
able to increase the rate of stimulation for a more effective frac, but there
were associated benefits of a more efficient frac timeline. By decreasing the
overall time on pad by 20%, the operator was able to effectively bring production
forward, resulting in an earlier time to cash. The operator also decreased
associated costs, such as operational day rates and equipment rentals, by
effectively shortening their time on pad while optimally completing the job.
The long game is efficiency and cost. If an operator can use
predictive analysis to develop or analyze a casing string that allows them to
reach maximum rates while remaining under top pressure restrictions, then frac
efficiency becomes a less volatile factor. With the potential for delays and
setbacks now reduced as a result of a more effective casing design, operators
can more accurately develop operational timelines and look at other aspects of
the completion process for cost savings.
It is also important to recognize that an unplanned rate reduction
not only affects frac efficiencies, but it also could affect well production. Verifying
that perforation velocities remain in the target range for maximum EUR is
imperative to the well’s success. Using the predictive pressure analysis tool
with a focus on casing optimization allows operators to accurately forecast
timelines, costs and efficiencies while knowing there will be little volatility
in the design they choose. WO
CAMERON HORNOR is a technical services adviser for Universal
Pressure Pumping in Midland, Texas. He began his career with Universal as a
field engineer in Connellsville, Pa., before transferring to Midland in 2021 as
a senior field engineer. Mr. Hornor graduated with a BS degree in petroleum and
natural gas engineering from West Virginia University in 2017.