Conventional cores, or whole cores, are solid cylinders of rock that can be brought to the surface as a single piece. These cores are used to model reservoir behavior to optimize production, based on the analysis of core porosity, permeability, fluid saturation, grain density, lithology and texture. However, the process of obtaining and analyzing cores is a notoriously costly one, calling for rig time, crew mobilization to site and subsequent analysis.
Drill cuttings, on the other hand, are removed from wells and brought to the surface in drilling mud and are often examined to make a mud log of the subsurface materials penetrated at various depths. Even though cuttings are basically the same material as cores, many operators have traditionally been suspicious of drawing reliable data and conclusions from drill cuttings.
The Cuttings Alliance, a consortium of Stratagraph, CoreSpec Alliance and PetroScale Reservoir Solutions, is working on shifting that attitude. The aim of these oil and gas service companies is to offer their clients information worthy of a coring job for a smaller price.
Stratagraph has been delivering mud logging, geosteering and wellsite supervision for more than 50 years, whereas CoreSpec’s specialty rock property testing goes beyond traditional cuttings analysis to create unique datasets. PetroScale uses geoscience, engineering and applied data analytics to determine reservoir and geomechanical properties. Within the Cuttings Alliance, Stratagraph is responsible for collecting a representative sample of the formation that has been drilled through, and Petroscale and CoreSpec handle all geophysical and geomechanical modeling.
Together, the team developed a process that provides true insight into a well to help the production model and inform future completion work in the same field.
With the industry shifting in recent years toward long horizontal drilling, operators are increasingly finding traditional core samples less meaningful, derived as they are from one distinct spot that may end up 7,000 ft away, laterally, from the continuation of the wellbore. Because cuttings are a natural byproduct of the drilling process, the Cuttings Alliance has devised a process that merely calls for the operator to collect what they already have—drill cuttings.
From that point on, the Cuttings Alliance manages all logistics and works together as one entity to bring mud logging, cuttings analysis and sophisticated well interpretation under one roof to reduce costs and improve well productivity in the field.
New analysis software
In recent years, myopic businesses have sold vast amounts of data into the oil and gas industry to a point where operators have acquired archives of data that are not realizing any return on investment. Operators either do not have time to action the data or they lack back-office personnel to use the data to produce executable decisions to optimize operations. If the data were properly harnessed, operators could derive better understanding of their reservoir, which in turn equates to better fluid and proppant programs, more efficient fracs and higher well productivity.
Since modern day operators possess reams of data but often lack the means of interpretation, RockProp was developed. This new software delivers analysis for cuttings, logs and drilling data. With traditional formation evaluations, an operator has to approach three different vendors: a mud logging company, a laboratory for sample analysis and a data interpretation service. Alternatively, by engaging with the Cuttings Alliance, the operator is afforded more control over its cuttings analysis workflow. The operator has access to a one-stop shop managing the migration of the cuttings from the well site to the laboratory and interpretation in a fully streamlined process, billed on a turnkey basis to further help operators predict and manage costs.
This approach improves overall process efficiency and creates an opportunity to remove three separate entities and their associated mark-ups and variations in quality standards to deliver meaningful, relevant and actionable information. At the end of their engagement with the Cuttings Alliance, the operator is not just provided with more data, but rather a set of conclusions that advise on which data are important and relevant to improve the operator’s completions and evaluations going forward.
Many operators have separate programs and budgets for mud logging, cuttings analysis and interpretation. RockProp brings these services together into a single product to save time and money while providing a sophisticated interpretation to improve reservoir characterization. RockProp combines log and drilling data with physical properties measured from cuttings to output reservoir parameters. Mineral models, total porosity, effective porosity and bound versus mobile fluid estimates are obtained. This provides an assessment along vertical or horizontal wellbores that is independent of log models, which can be used to refine 2D and 3D reservoir models, improve geosteering, optimize completion designs and better characterize well potential.
In practice in the US
The Cuttings Alliance formed a relationship with an Eagle Ford operator that was able to supply the team with extremely useful data. Instead of analyzing broadly spaced samples, the operator had analyzed every sample. As a result, the Cuttings Alliance was able to validate its mineral model, along with its porosity and fluid models, by looking back and comparing the results to what the operator actually did, observing a match in the two and devising a set of recommendations as a result. By engaging closely with the operator and demonstrating the model, the Cuttings Alliance was able to prove the validity of the method.
As the whole process matures, fewer samples will need to be taken, bringing down associated costs even further.
More recently, the Cuttings Alliance has engaged RockProp in vertical wells in the Delaware Basin area of the Permian Basin: an area with complex petrophysical issues. The operator has, to date, invested significant expenditure on wireline logs and other types of measurements to understand nuances and variability within its pay sections. By deploying the RockProp service in this case, the operator expects to save approximately $200,000 per well, with the data providing even more value at the completion phase.
Frac and completion jobs can represent up to 70% of the costs of the well. If an operator can save one or two frac stages at least, they could save upward of $500,000.
RockProp is in the early phase but will serve as an enhancement or even a replacement to extremely expensive logging programs in appraisal and development assets from a reservoir characterization perspective. This interpretive deliverable will be rounded out with innovation in the geomechanics space as well, where a reservoir is addressed from a mineralogical perspective and with data that would impact completions. Reducing pressure on an operator’s completion budget is an ongoing area of development, with the goal of obtaining additional information from RockProp analysis of the cuttings and developing completion fluid programs from the data, enabling clients to cut their fluid budgets significantly.
In the current economic environment, there is hesitation about expenditure on scientific analysis. As such, fewer rock samples are being taken for direct measurement and calibration. Although less data can be derived from cuttings in comparison with a whole core, experience has demonstrated that when coupled with secondary calibration data or mud logging data, a strong model can be built to the extent that the cuttings can be used to improve engineering solutions and remove a tremendous amount of cost from drilling operations.
Essentially, the Cuttings Alliance creates a workflow and a program that can help operators reduce costs, while still maintaining the quality of data that are required to properly develop an asset.
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