About

A. Daniel Hill is a Professor of Petroleum Engineering at Texas A&M University, holding the Noble Chair and serving as a Regents Professor. He earned his B.S. in Chemical Engineering from Texas A&M University in 1974, followed by an M.S. in Chemical Engineering in 1976 and a Ph.D. in Chemical Engineering from the University of Texas at Austin in 1978. His research interests include oil recovery and well injection processes, with a focus on production engineering, well completions, well stimulation, production logging, and complex well performance, including horizontal and multilateral wells. Dr. Hill holds five patents related to these areas and is recognized as an industry expert. He has received numerous awards and honors, including the John Franklin Carll Award and the Gulf Coast Regional Distinguished Achievement Award from the Society of Petroleum Engineers, and has served as a director for the Society of Petroleum Engineers Board of Directors.

Research topics

• Computer Science
• Petroleum engineering
• Chemistry
• Geotechnical engineering
• Materials science
• Forestry
• Composite material
• Geography
• Geology
• Engineering

Selected publications

• Evaluation of Perforation Erosion and Fluid Allocation with Distributed Acoustic Sensing in Multi-Stage Fracture Stimulation

  SPE Hydraulic Fracturing Technology Conference and Exhibition · 2025-01-28 · 3 citations

  article

  Abstract Limited entry design has been utilized to enhance distribution of fracture fluid and proppant across clusters in multi-stage fracture stimulation for horizontal wells. The concept uses limited perforation diameter/number to generate perforation frictional pressure drop to control fluid distribution through perforations, and the goal is to evenly distribute fracture fluid over all clusters. However, in today's field practice, high injection rate and large volume of proppant injection often lead to severe erosion of the perforations, resulting in reduced perforation friction and lower fracturing efficiency. Distributed Acoustic Sensing (DAS) positioned behind the injection wellbore monitors acoustic vibrations generated by slurry injection at the clusters in real time. This enables monitoring and evaluating of the dynamic changes in perforation size and slurry distribution, as indicated by the decay of the DAS signal. This paper presents a methodology that qualitatively determines the fluid distribution and perforation size for individual clusters using field DAS data. A correlation between the perforation diameter, flow rate and the induced sound pressure intensity are developed based on Computational Fluid Dynamics (CFD) acoustic simulation results. By integrating the acoustic correlation and the wellbore energy balance equation, slurry distribution and perforation size at clusters are simultaneously calculated at every time step in a multi-cluster stage. This calculation is repeated until the end of the treatment, and the cumulative fluid allocation and the post-fracture perforation size are estimated. The correlation is applied to a field DAS data set. The estimated eroded diameters are compared with post-fracture perforation images taken by a downhole video camera. The estimated cumulative fluid volumes are compared with the interpretation of Distributed Temperature Sensing (DTS). In both datasets, the overall trends are consistent. Two clusters where the perforations were heavily eroded are identified by the DAS interpretation. These comparisons and the agreements of the results support the validation of the new acoustic correlation and the new DAS interpretation methodology. The DAS interpretation methodology helps observe the process of perforation erosion and understand its mechanism, leading to an improvement of perforation design.

  PublisherDOI

• Evaluating Fluid Distribution by Distributed Acoustic Sensing (DAS) with Perforation Erosion Effect

  Sensors · 2025-11-18 · 2 citations

  articleOpen accessSenior author

  Among the various completion strategies used in multi-stage hydraulic fracturing of horizontal wells, the limited entry design has become one of the most common approaches to promote more uniform slurry distribution. This method involves reducing the number of perforations so that higher perforation friction is generated at each entry point. The increased pressure drops force fluid and proppant to be diverted across multiple clusters rather than concentrating at only a few, thereby enhancing stimulation efficiency along the lateral. In this study, Computational Fluid Dynamics (CFD) simulations were performed to investigate how perforation erosion influences acoustic signals measured by Distributed Acoustic Sensing (DAS). Unlike previous studies that assumed perfectly circular perforations, this work uses oval-shaped geometries to better reflect the irregular erosion observed in the field, which provides more realistic modeling. The workflow involved building wellbore and perforation geometries, generating computational meshes, and solving transient turbulent flow using Large Eddy Simulation (LES) coupled with the Ffowcs Williams-Hawkings (FW-H) acoustic model. Acoustic pressure was then estimated at receiver points and converted into sound pressure level for analysis. The results show that, for a given perforation size, changes in flow rate cause log(q) versus sound pressure level to follow a straight line defined by a constant slope and varying intercept. Even when erosion alters the perforation into an oval shape, the intercept increases logarithmically, resulting in reduced sound amplitude, while the slope remains unchanged. Furthermore, when the cross-sectional area and flow rate are equal, oval perforations produce higher sound amplitudes than circular ones, suggesting that perforation geometry has a measurable influence on the DAS signal. This indicates that even when the same amplitude DAS signal is obtained, assuming circular perforations when estimating the fluid distribution leads to an overestimation if the actual perforation shape is oval. These findings highlight the importance of considering irregular erosion patterns when linking DAS responses to fluid distribution during hydraulic fracturing.

  PublisherOA PDFDOI

• Impacts of Near and Far-Field Diverters on Proppant Transport in Complex Fracture Systems

  SPE Hydraulic Fracturing Technology Conference and Exhibition · 2025-01-28 · 1 citations

  article

  Abstract During hydraulic fracturing, temporarily plugging existing fractures and diverting the injected slurry further into newly created fractures is beneficial for maximizing reservoir contact and productivity. Typically, the injected slurry flows into the path of least resistance, which may not always align with the targeted stimulation zones. Consequently, this can result in leaving many created fractures inadequately propped, as much of the injected proppants settle near the wellbore or are lost in the overtreated fractures. To understand maximizing the fracture-propped area and the transport of the injected fluid and proppant into both nearby and distant fractures, various diverters were tested in this experimental work. The aim was to investigate the plugging behavior of near-wellbore and far-field diverters and determine the associated proppant transport within a complex slot system. A laboratory-scale slot apparatus was used to investigate the plugging behavior of injected diverters within both smooth- and rough-wall surfaces. The apparatus consisted of a 4-ft.-long primary fracture and 1-ft. secondary fracture located 2 ft. from the injection point. The roughness of the wall surface was achieved using 3D-printing technology to mimic an actual fractured core sample. Both smooth- and rough-wall surface apparatuses were set at fracture widths of 0.2 in. for the main slot and 0.1 in. for the side slot. Fresh water and 100-mesh sand (2.65 SG) were tested with one near-wellbore diverter and two different far-field diverters. The near-wellbore diverters consisted of cylindrical pellets, while the far-field diverters were in powder form. The diverters were tested at room temperature by mixing both near- and far-field diverters without sand and pumping them into the slot system, followed by pumping the sand separately. Lab results show the injected near-wellbore diverter effectively plugged most of the main fracture and caused different dune shapes to form associated with the fracture-wall roughness. The near-wellbore diverter also accumulated and blocked the majority of the secondary fracture inlet. No near-wellbore diverters entered or were transported into the secondary fracture due to the pellet's size compared to the width of the secondary fracture. In the case of the rough-wall fractures, the far-field diverters contributed to plugging most parts of both the main and side fractures, as these materials expanded with an increase in the mixing time. The injected diverters helped divert the injected sand, resulting in most of the sand being transported further, and outside, of the slots. Only a small amount of the injected sand settled inside the fracture slots, as most of the cross-sectional flow area was plugged by the diverters. Sand turned into the secondary slot only through a small opening, without forming a clear sand dune as was observed without diverters. Overall, both near- and far-field diverters provided more effective plugging in the rough-wall fractures compared to the smooth-wall fractures.

  PublisherDOI

• Experimental Investigation of Degradable Solids Diverter Efficiency for Different Completions Used in Matrix Acid Stimulation

  2024-11-04 · 1 citations

  article

  Abstract A known challenge in carbonate acid stimulation is achieving a uniform acid distribution in long wells along a heterogeneous reservoir. Completion strategies such as running a limited-entry-liner may not be sufficient to achieve the desired conformance. In recent years, degradable solids have become one of the most common diverters for acid stimulation. However, their behavior in uncemented completions is not well understood. In this study, parallel dual-core flow tests were conducted to evaluate the impact of completion type (cased hole vs. open hole) on diverter efficiency. In the dual-core flow setup, two limestone cores with a permeability ratio of 30:1 were used, and experiments consisted of three main flow stages. First, 15wt% HCl was injected, which tended to create a wormhole in the high-perm core. A specified volume of a solids diverter slurry was then injected to improve the flow distribution. The final stage consisted of injecting 15wt% HCl until breakthrough. The flow rate of each core was recorded throughout the test to evaluate the diversion effect for both open hole and cased hole completion scenarios. CT scans of both cores were obtained to visualize the wormhole geometry after each acid stage. Test results showed significantly different diverter performance for the cased hole vs. open hole scenarios, leading to insightful guidelines on diverter efficiency depending on completion type. After the first acid stage, a dominant wormhole was created in the high-perm core only, mainly due to the large permeability ratio. This behavior was very similar for both completion scenarios. In the open-hole test, the diverter formed an external filter cake on the injection face of the high-perm core. The second acid stage easily broke through this external filter cake and continued to propagate the original wormhole. As a result, acid diversion was limited, and a relatively short wormhole was created in the low-perm core. However, in the cased-hole test, a relatively higher volume of diverter entered the perforation / wormhole structure, leading to a more effective diversion and hence a more even stimulation of both cores after the second acid stage was injected. The large-scale dual core flow setup in this study is the first of its kind and using it in conjunction with the implemented workflow has provided valuable insights into how various completion types will impact solids diverter efficiency during matrix acid stimulation. As completion lengths continue to get longer, a good understanding of solids diverter efficiency, especially for open hole completions currently being implemented in the Middle East, is necessary to develop reliable models that can be used for a more effective treatment design.

  PublisherDOI

• Experimental Evaluation of Lactic Acid for Matrix Acidizing of Carbonates

  SPE Journal · 2024-11-18 · 1 citations

  article

  Summary To improve the efficiency of standard hydrochloric acid (HCl) stimulation treatments, many alternative acid systems have been developed to mitigate corrosion, increase wormhole efficiency, and divert fluids for better acid coverage. However, these alternative systems come at a price compared with HCl, which is cheaper and sufficient in most applications. Lactic acid is an organic acid that is less corrosive and has reduced reactivity compared with HCl. The advantages and application of lactic acid have not been studied extensively like other alternative acids. To evaluate lactic acid as a viable alternative acid system, we conducted a series of linear coreflood matrix acidizing experiments using Indiana limestone rock samples with 40 wt% lactic acid at two temperatures over a range of injection rates. The goal was to characterize the wormholes created by lactic acid and identify the appropriate condition that lactic acid can outperform HCl. Coreflooding tests were also conducted at high temperatures and lower concentrations to observe a change in behavior and performance. Lactic acid performance was analyzed by comparing pore volumes (PVs) to breakthrough (PVbt) with previous HCl experiments. Because HCl exhibits low efficiency when injected below the optimal condition, lactic acid was found to be more efficient than HCl at injection rates below optimum for 40 wt%. At a temperature of 150°F, lactic acid maintained similar PVbt over the range of injection rates. Wormhole geometry from computed tomography (CT) imagery and pressure response data was studied to identify unique characteristics or behaviors of lactic acid. CT images of lactic acid-generated wormholes reveal a geometry vs. injection rate relationship that is contrary to the conventional understanding of wormhole growth patterns. The images show extensive branching in most low injection rate tests. The results are characterized as appearing to have self-diverting behavior. At an elevated temperature of 240°F, precipitation of lactic acid after reacting with calcium carbonate became visible. Pressure differential data across the core showed the pressure drop increased in nearly every experiment. When lower lactic acid concentrations were used, the pressure differential increase was not observed. Precipitation occurred during and immediately after most high-temperature experiments, and when the concentration is above 30 wt%, it is suspected to be plugging permeable channels. The study concludes that at a temperature of 150°F (relatively low compared with 240°F), lactic acid has advantages in wormhole efficiency when compared with HCl. Combined with less corrosiveness to the well tubulars and surface equipment, lactic acid can be a good chemical system for carbonate acidizing. For high-temperature formation, lower concentration lactic acid can be used as long as wormhole efficiency is not compromised. It is recommended that for each specific reservoir formation, the appropriate lactic acid concentration should be identified from laboratory tests to ensure the stimulation efficiency, avoid detrimental precipitation, and save operation costs.

  PublisherDOI

• Experimental Investigation Using Low-Frequency Distributed Acoustic Sensing for Two Parallel Propagating Fractures

  SPE Hydraulic Fracturing Technology Conference and Exhibition · 2024-01-30 · 2 citations

  articleSenior author

  Abstract Low-frequency distributed acoustic sensing (LF-DAS) is a diagnostic tool for hydraulic fracture propagation in the far-field using measured values of strain. To understand subsurface conditions with multiple propagating fractures, a laboratory-scale hydraulic fracture experiment was performed to simulate the LF-DAS response to fracture propagation with embedded distributed optical fiber strain sensors under these conditions. The objectives of this research are to generate two hydraulic fractures of known geometry, measure the strain response along distributed fiber sensors embedded in the sample, and use the results to improve interpretations of field LF-DAS data when multiple fractures are approaching an observation well. The experiment was performed using a transparent 8-inch cube of epoxy with two-parallel radial initial flaws centered in the cube 2.6-inches apart. Fluid was injected into the sample to generate fractures along the initial flaws. The experiment used distributed high-definition fiber optic strain sensors with tight spatial resolutions. The sensors were embedded at two different locations on opposite sides of the initial flaws, serving as observation/monitoring locations. Pressure and fracture propagation were also recorded. This paper presents a workflow to model fracture geometries, and simulate the resulting strain along a fiber optic sensor. We employed finite element modeling to numerically solve the linear elastic equations of equilibrium continuity and stress-strain relationships. The simulation domain includes one-half of the 8-inch epoxy cube with two radial fractures. The measured strains from the experiment were compared to simulation results from the finite element model. The experimentally derived strain and strain-rate waterfall plots from this experiment show responses to both fractures propagating, while the fracture below took most of the fluid during the experiment. Interestingly, a fracture first began propagating from the upper of the two flaws, but once the lower fracture was initiated, it grew much more than the upper fracture. Both fibers were intercepted by the lower fracture, further verifying the strain signature as a fracture is approaching and intersecting an offset fiber. The zero-strain-rate method was applied to both fibers to dynamically estimate the propagation of the fracture fronts as they approached the fibers. The fracture growth behavior interpreted with the zero-strain-rate method compared well to the evolving fracture dimensions obtained from video-recording of the fracture geometries. The results from this work can be used in the field to reveal stress shadowing effects of two fractures and further increase our understanding of how LF-DAS can be used in the field to diagnose fracture propagation when multiple fractures are approaching an observation well.

  PublisherDOI

• Experimental Investigation of Low-Frequency Distributed Acoustic Sensor Responses to Two Parallel Propagating Fractures

  Sensors · 2024-06-15 · 5 citations

  articleOpen accessSenior author

  Low-frequency distributed acoustic sensing (LF-DAS) is a diagnostic tool for hydraulic fracture propagation with far-field monitoring using fiber optic sensors. LF-DAS senses strain rate variation caused by stress field change due to fracture propagation. Fiber optic sensors are installed in the monitoring wells in the vicinity of a fractured well. From the strain responses, fracture propagation can be evaluated. To understand subsurface conditions with multiple propagating fractures, a laboratory-scale hydraulic fracture experiment was performed simulating the LF-DAS response to fracture propagation with embedded distributed optical fiber strain sensors under these conditions. The experiment was performed using a transparent cube of epoxy with two parallel radial initial flaws centered in the cube. Fluid was injected into the sample to generate fractures along the initial flaws. The experiment used distributed high-definition fiber optic strain sensors with tight spatial resolutions. The sensors were embedded at two different locations on opposite sides of the initial flaws, serving as observation/monitoring locations. We also employed finite element modeling to numerically solve the linear elastic equations of equilibrium continuity and stress-strain relationships. The measured strains from the experiment were compared to simulation results from the finite element model. The experimentally derived strain and strain-rate waterfall plots from this study show the responses to both fractures propagating, while the fracture at the lower position took most of the fluid during the experiment. Interestingly, a fracture first began propagating from the upper flaw of the two flaws, but once the lower fracture was initiated, it grew much faster than the upper fracture. Both fibers were intercepted by the lower fracture, further verifying the strain signature as a fracture is approaching and intersecting an offset fiber.

  PublisherOA PDFDOI

• Investigation of the Reduction in Distributed Acoustic Sensing Signal Due to Perforation Erosion by Using CFD Acoustic Simulation and Lighthill’s Acoustic Power Law

  Sensors · 2024-09-16 · 4 citations

  articleOpen accessSenior author

  Distributed Acoustic Sensing (DAS), widely adopted in hydraulic fracturing monitoring, continuously measures sound from perforation holes due to fluid flow through the perforation holes during fracturing treatment. DAS has the potential to monitor perforation Tulsa, OK 74136erosion, a phenomenon of increasing perforation size due to sand (referred to as proppant) injection during treatment. Because the sound generated by fluid flow at a perforation hole is negatively related to the perforation diameter, by detecting the decay of the DAS signal, the perforation erosion level can be estimated, which is critical information for fracture design. We used a Computation Fluid Dynamics (CFD) acoustic simulator to calculate the acoustic pressure induced by turbulence inside a wellbore and investigated the relationship between the acoustic response from fluid flow through a perforation and the perforation size by running the simulator for various perforation diameters and flow rates. The results show that if the perforation size is constant, the plot between the calculated sound pressure level and the logarithm of flow rate follows a straight line relationship. However, with different perforation sizes, the intercept of the linear relationship changes, reducing the sound pressure level. Lighthill’s power law indicates that the change in intercept corresponds to the logarithm of the ratio of the increased diameter to the original diameter. The reduction in sound pressure level observed in the CFD simulation correlates with the reduction in the DAS signal in field data. The findings of this study help to evaluate perforation diameter growth using DAS and interpret fluid distribution in fracture stimulation.

  PublisherOA PDFDOI

• Field Application of a Novel Multiresolution Multiwell Unconventional Reservoir Simulation: History Matching and Parameter Identification

  SPE Journal · 2024-02-16 · 9 citations

  articleSenior author

  Summary This study focuses on developing an efficient workflow by integrating a multiresolution simulation model and a multiobjective evolutionary algorithm (MOEA) for application to multiwell unconventional reservoirs. In this approach, hydraulic fractures are represented using a dual porosity, dual permeability system facilitated by an embedded discrete fracture model (EDFM). A novel fast-marching simulation method is used to cut down on computational expenses by an order of magnitude, greatly accelerating the history-matching process. A variety of integrated monitoring technologies were implemented to map out the hydraulic fracture network. Insights into hydraulic fracture locations were gleaned from warm-back analysis of distributed temperature sensing data, and these locations were then assimilated into the simulation model as embedded discrete fractures. For the simulation, a fast-marching-based multiresolution model was used to partition the reservoir into local and shared domains guided by the diffusive-time-of-flight (DTOF) principle. The local domain maintained the original 3D grids near the wells while transforming the remaining area into 1D grids to accelerate the simulation process. Before history matching, a thorough sensitivity analysis was conducted to pinpoint the most impactful parameters. Subsequently, the model was fine-tuned using production data through an MOEA. The most sensitive parameters in history matching were identified as fracture geometry and conductivity, fluid saturations, and rock compressibility in the stimulated reservoir volume (SRV) areas. After history matching, there was a noteworthy reduction in the uncertainty of these tuning parameters. The calibrated parameters are valuable to evaluate the effectiveness of the well completion design. Overall, this work emphasizes the innovative combination of techniques applied, the efficiency gains in the history-matching process, and the scalability of the approach to other oilfield applications.

  PublisherDOI

• OS01-12 A computational toolbox supporting the development of Safe and Sustainable by Design chemicals and materials

  Toxicology Letters · 2024-09-01 · 2 citations

  article
  PublisherDOI

Frequent coauthors

• Ding Zhu

  503 shared

• H. A. Nasr‐El‐Din

  Texas A&M University

  61 shared

• Shohei Sakaida

  Chevron (United States)

  40 shared

• Mateus Palharini Schwalbert

  Petrobras (Brazil)

  27 shared

• Donghui Zhu

  Stony Brook University

  21 shared

• Xiaosi Tan

  Southeast University

  20 shared

• Smith Leggett

  Texas Tech University

  20 shared

• Kenji Furui

  Waseda University

  20 shared

Labs

• Research LaboratoriesPI

Awards & honors

• John Franklin Carll Award, Society of Petroleum Engineers (2…
• Gulf Coast Regional Distinguished Achievement Award, Society…
• Pipeline Award, Society of Petroleum Engineers (2012)
• Production and Operations Award, Society of Petroleum Engine…
• Honorary Membership, Society of Petroleum Engineers (2020)