Executive Summary

The COVID-19 pandemic has changed the way we live, especially in the oil and gas industry. Thousands of talented professionals and experts have left our industry in the last few months. Many of them will not return. It becomes more difficult than before for our associate editors to find qualified technical reviewers. Our associate editors and technical reviewers have done a great job even during this difficult period. Their efforts are greatly appreciated!


The original influx-management envelope (IME) developed by Culen et al. is a decision-making tool for how to deal with an influx during managed-pressure-drilling (MPD) operations that offers a substantial improvement over the traditional MPD well-control matrix (WCM). In the paper The Influx-Management Envelope Considering Real-Fluid Behavior, the authors find that the simplified analytical solution in IME is inaccurate for many real-world applications. Therefore, they extend the original IME by deriving the underlying equations from first principle without making the simplifying assumptions and considering the gas migration in the annulus as a single bubble. The proposed approach is faster and more accurate than the original IME.

Biot’s coefficient plays an important role in solving many practical petroleum-engineering problems, including, for example, the design of hydraulic-fracturing jobs and the estimation of in-situ closure stress on proppant. In the paper entitled A Correlation for Estimating the Biot Coefficient, the authors develop a new method for estimating the Biot coefficient in conventional and unconventional (tight and shale) reservoirs on the basis of knowledge of the ratio of permeability to porosity (k/f) and the pore-throat radius (rp35). The overall approach allows the integration of geomechanics with flow units, geology, petrophysics, and reservoir engineering. The developed method is validated by testing.

The paper entitled Silica and Graphene Oxide Nanoparticle Formulation To Improve Thermal Stability and Inhibition Capabilities of Water-Based Drilling Fluid Applied to Woodford Shale evaluates the potential of using silica (SiO2) nanoparticles (NPs) (SiO2-NPs) and graphene nanoplatelets (GNPs) as drilling-fluid additives in a single formulation to improve shale inhibition and long-term stability of water-based mud (WBM) against temperature effects. This investigation supports the potential use of nanomaterials to enhance the inhibition capabilities and the long-term stability of WBM for unconventional shales, presenting an environmentally friendly alternative for harsher environments.

Mud losses are frequently observed when drilling in depleted formations. In the paper entitled Understanding Loss Mechanisms: The Key to Successful Drilling in Depleted Reservoirs?, the authors investigate several mechanisms that might be responsible for the elevated risk of mud losses in differentially depleted sand/shale sequences. Numerical models of synthetic cases representative of lost-circulation scenarios in a high-pressure/high-temperature (HP/HT) field in the North Sea, under normal faulting conditions, are set up using the finite-element method. The results from the study are important for establishing best practices when drilling in depleted formations.

An accurate estimation of pore pressure allows a more efficient casing seat design. Commonly used methods are based on sonic-wave velocity and formation-resistivity factors. In the paper entitled A Pore-Pressure Equation for Carbonates, a new equation for estimating pore pressure for carbonates is developed. The new equation is a function of the differential stress and a porosity-relative constant that depends implicitly on carbonate-rock compressibilities. Two case studies in carbonates from Mexico are presented to demonstrate the viability of the equation.

In the paper, A Switching MPD Controller for Mitigating Riser Gas Unloading Events in Offshore Drilling, the authors present a novel MPD approach for riser gas unloading control that makes use of a pressurized riser drilling (PRD) controller. The control algorithm considers the pressure limits of the riser and of the openhole formations and can adjust for kick uncertainties. The proposed PRD controller consists of three operation modes: pressure control mode, flow control mode, and solubility control mode, with each mode applicable to its corresponding operating condition. Simulation results show that the proposed controller can quickly and robustly control the riser gas unloading situations with complicated transient conditions, without fracturing downhole formations or jeopardizing the pressure integrity of the riser.


Perforation is widely used in low-permeability reservoirs. The productivity calculation after perforation completion is challenging because of the seepage characteristics of low-permeability reservoirs. In the paper entitled Calculation of Perforated Vertical and Horizontal Well Productivity in Low-Permeability Reservoirs, the authors propose the productivity formulas of perforated horizontal wells in a low-permeability reservoir based on the triple-radial-flow model. The formulas are derived considering the cases of the damaged zone being penetrated and being partially penetrated. Factors affecting productivity are studied in the paper.

In permanently abandoned wells, cement plugs serve as a well-barrier element that is essential for providing long-term zonal isolation. The paper entitled The Effect of Casing-Pipe Roughness on Cement-Plug Integrity investigates the influence of downhole-pipe roughness to the hydraulic sealing of a cement plug. CFD simulation and experimental tests show that placing cement plugs in rough-surface pipes could reduce the gas-leak rate.

Void spaces might form in gravel packs during gravel-pack installation and the production life span of the well in sand-control completion. These voids provide permeable channels within the pack that allow sand to pass into the wellbore that consequently lowers the pack efficiency. The paper entitled Gravel-Packing Experiments with Oil-Swelling Rubber Particles introduces a modified design for gravel packing with oil-swelling rubber particles. The new pack is composed of gravel- and oil-swelling rubber particles capable of preventing the voids from forming and maintaining pack tightness rather than 100% gravel. The results show that gravel/rubber-particle packs have promising permeabilities and reasonable expansion potential to fill the voids.

To provide a long-term zonal isolation, the cement sheath should be designed to work throughout the entire lifetime of a well. The paper entitled New Materials and Technologies for Life-Lasting Cement Sheath: A Review of Recent Advances provides a review of advances in applications of nanomaterials and new technologies in oil/gas well cementing. The authors discuss how these new materials and technologies can be the solution for providing a life-lasting cement sheath, through enhanced performance of the cement sheath with reasonable cost and minimized environmental effect, both of which have high importance in the oil/gas industry.

The paper entitled 3D Geomechanical Evaluation of Jetting Operations for Producing Hydrate Chimneys in the Sea of Japan presents a 3D geomechanical simulation study to evaluate the feasibility of the jetting method to produce methane from the hydrate chimneys in the Sea of Japan. In this work, the authors construct three types of 3D geomechanical models to represent three shallow-methane-hydrate-inhabitation types (chunk, laminated, and dispersed) by using data from various sources. This numerical simulation evaluates potential risks related to jetting operations of hydrate chimneys in the Sea of Japan and provides critical information for the engineering design of the proposed field test of jetting operations to produce this valuable resource in the Sea of Japan. 

The paper entitled Mud/Cement Displacement in Vertical Eccentric Annuli presents an analytical method for the solution of cement/mud displacement and evaluation of interfluid contamination during displacement in vertical eccentric annuli. The work aims to take part in addressing the undeniable importance of a complete cement displacement by means of a semianalytical solution for the fluid displacement coupled with the interface-instability analysis, attempting to provide a realistic prediction of the amount of interfluid mixing and cement contamination, along with qualitative judgements on the quality of the cementing job. This methodology is intended to offer improvement techniques for the displacement and provide enhancements for practical industrial applications.

Shilin Chen, SPE Drill & Compl Executive Editor,
Chief Technical Advisor, Halliburton Drill Bits and Services