The Devonian-Mississippian STACK/SCOOP Play of the Oklahoma Anadarko Basin is a complex assemblage of tight carbonate and siliciclastic strata and an important oil and gas province. In the last decade, prolific drilling has demonstrated significant heterogeneity in the composition of oils produced from STACK/SCOOP reservoirs. This study discusses possible geoscientific explanations for the heterogeneity observed in produced oils and describes how source, maturation, and migration affect their composition.
Geochemical data from 136 produced oils across 12 counties from 4 producing reservoirs is reviewed. Calculated thermal maturity (Rc%) from alkylated polyaromatic compounds shows excellent agreement with oil thermal maturity increasing with increased depth. Oils produced from overpressured reservoirs exhibit a strong relationship between Rc% and Gas-Oil Ratio (GOR), while normal- to underpressured reservoirs exhibit GORs up to an order of magnitude higher at similar Rc%. Light hydrocarbons show that paraffinicity varies starkly with producing reservoir, suggesting compositional fractionation from diffusive migration through tight and argillaceous strata. Conversely, aromaticity varies geographically by Play Region, indicative of changing depositional environments and organic input across the basin. Isoprenoid and sesquiterpane biomarkers indicate all oils are generated by Type II or Type II/III mixed organic matter, but Springer Group reservoirs are charged by a highly argillaceous, non-Woodford source.
The Anadarko Basin is the deepest sedimentary basin in the cratonic interior of the North America with as much as 40,000 feet of Paleozoic sediments (Johnson, 1989). The Anadarko is an asymmetric basin with the deepest sediments bound against the Amarillo-Wichita Uplift to the southwest. The basin is elongated along its west-northwest axis and bound by the Nemaha Ridge to the east and the Anadarko shelf to the west and north.
In the last decade, drilling of Devonian-Mississippian strata along the margins of the basin have delineated one the continent's most successful petroleum resource plays. These areas are colloquially referred to as the
We describe a case study to extract meaningful geological information from a modern high-fold seismic dataset in the north-east Delaware basin. The target of the study is the heterogeneous geology of the Bone Spring and Wolfcamp Formations. A database of well data was used to understand the variation in elastic properties in terms of geological changes that include: mineralogy, organic content and the likely onset of over-pressure. The geology was represented by a set of 5 elastic facies: carbonates, calcareous mudstones, siliciclastics, organic-rich and clay-rich shales. The well data were also used to calibrate seismic amplitudes prior to performing a Bayesian pre-stack inversion to solve for estimates of facies and impedances. The results are shown to provide insights into the regional stratigraphic deposition and evolution of the formations, including mapping of discontinuous carbonate and high TOC intervals. The property volumes are the starting point for future predictive geological, formation-pressure and stress models for informing optimal resource exploitation within the study area.
The geology of the Delaware Basin is heterogeneous in both lateral and vertical directions. Understanding the geological complexity is critical for optimizing exploitation strategies in both the Bone Spring and Wolfcamp Formations. Seismic data provide valuable spatial information between and away from well locations, however, the process of extracting the geological information from the seismic amplitudes is non-trivial. In this paper, we describe a state-of-the-art pre-stack seismic inversion study in the north-east Delaware Basin, with the objective of obtaining reliable estimates of the geology across the 380 square mile study area, Figure 1.
Charzynski, Katarzyna (UpCurve Energy LLC) | Faith, Kristi (UpCurve Energy LLC) | Fenton, Zach (UpCurve Energy LLC) | Shedeed, Ahmed (UpCurve Energy LLC) | McKee, Michael (Jetta Permian, LP) | Bjorlie, Sid (Jetta Permian, LP) | Richardson, Michael (Jetta Permian, LP)
Numerous horizontal Wolfcamp completions have encountered H2S and excessive water in Reeves County, Texas. Anecdotal theories have attributed the source to deep Paleozoic faulting, fluids in Bone Spring sands or untreated frac fluids. The objective of this project is to identify the source of these issues and enhance oil productivity by eliminating or greatly reducing excessive water and H2S in horizontal Wolfcamp wells.
Narrow parallel Delaware Mountain Group (DMG) (Figure 1) grabens are seismically mapped and extend across the area of interest 44 square mile (AOI). The orientations rotate from N104E in the northern mapped area to N136E in the southern mapped area. Some wells drilled beneath these shallow lineaments produce high levels of H2S and have anomalously high water oil ratios (WOR). Frac gradient (FG) departures of greater than −0.1 psi/ft were observed to align beneath the shallow mapped features of numerous Wolfcamp horizontals with elevated levels of H2S and high chloride produced water. It is hypothesized that these mapped graben features are the shallow expression of vertical fractures. These low-pressure fracture zones are a conduit for H2S and high chloride water production in the Wolfcamp. The features can be interpreted seismically on the DMG level, but there is a great deal of uncertainty in determining the extent of the vertical fracturing. Pre-stack HTI Velocity Variation with Azimuth (VVAZ) analysis of long offset modern 3D seismic data is utilized to locate these fracture corridors at the Wolfcamp horizons.
Initial recognition of the low frac gradient correlation to the shallow seismic lineament prompted analysis of DFITs, frac treating pressure data, and fluid tracers to improve the understanding of this relationship in order to better manage the impact on production from Wolfcamp wells. In existing wells with impaired production, bridge plugs were set on the heel side to isolate the zones of low frac gradients and successfully eliminated H2S and excessive water. The durability of this isolation within the wellbore has up to 2 years of production history without the return of H2S or excessive water.
Precise pre-drill identification of these shallow graben features at the horizontally targeted horizons benefits production, development planning, and completion strategies by reducing or eliminating frac connections to H2S and excessive water. Limiting the connection to the vertical fracture zones reduces associated lease operating expense via less water and H2S, allowing operators to maximize acreage that can be economically developed. Interpretation of the shallow features creates development plans that minimize negative impact of low-pressure zones and produce highly economic wells across these features by selectively skipping the completion around them.
Yassin, Mohamed A. (Geosciences Department, CPG, KFUPM, Dhahran Saudi Arabia) | Abdullatif, Osman M. (Geosciences Department, CPG, KFUPM, Dhahran Saudi Arabia) | Makkawi, Mohammad H. (Geosciences Department, CPG, KFUPM, Dhahran Saudi Arabia) | Yousif, Ibrahim M. (Geosciences Department, CPG, KFUPM, Dhahran Saudi Arabia) | Osman, Mutasim S. (Geosciences Department, CPG, KFUPM, Dhahran Saudi Arabia)
Well exposed Jurassic outcrops belt in central Saudi Arabia provides good outcrop analogs which can be utilized to capture the high resolution facies types and architecture that might help to fill the inter-wells gap in the subsurface. This study is focused on the characterization and modeling the facies types, body geometries deposited in geomorphic elements of carbonate ramp system and the distribution of the reservoir properties on it. Three-dimensional models for the different facies-body geometries were conducted to provide accurate stochastic representation. This study was conducted at a selected Jurassic outcrop reservoir analog that exposed around Riyadh area. The Mesozoic carbonate strata of central Saudi Arabia are interpreted to have been deposited in ramp systems and exposed in hundreds of kilometers in the strike and dip direction of palaeoshoreline. The study integrates detailed sedimentological and stratigraphic analysis from outcrop strata to capture facies-body geometries and their petrophysical properties on the ramp system. Nine lithofacies were interpreted from the stratigraphic sections. Spatially, the porosity and permeability show different ranges of heterogeneity from micro to meso and macro scales. Laterally, the reservoir properties show steady variations in contrast with the abrupt change vertically. This variation seems to be related to the sedimentary structure, grain size, and degree of cementation. Different pore types were recognized in the studied intervals, which include fracture, intraparticle, moldic and intercrystalline porosities. Several 3D facies models were constructed using sedimentological and stratigraphic data that collected from the field. These models express the complex and heterogeneous relationship between facies-body geometries in the outcrop precisely. Integration of these data to subsurface equivalent reservoirs will provide qualitative and quantitative information useful for understanding and predicting reservoir quality and architecture in carbonate ramps.
Shallow drilling losses are a significant problem in the Permian basin because of the presence of subsurface karst features. Karst weakens the soluble rock producing voids and caves systems that result in drilling losses. An operator drilling in Culberson County, Texas recently experienced total losses drilling four surface holes in a pair of neighboring pads located in bordering leases. Drilling into caves negatively affected operations by reducing the drilled footage per day, increasing fluid and cementing costs, and increasing the difficulty in performing satisfactory cementing jobs to cover the water table.
This paper will describe the issues faced drilling with losses and explain how to manage the risk of losses by improving surface well placement with airborne gravity full tensor gradiometry (FTG) to map subsurface hazards.
Airborne gravity FTG measures the directional components of the gravity field. Multiple simultaneously acquired tensor components allow identification of anomalies associated with subsurface voids. For this project, a Basler BT67 aircraft acquired data over the targeted expanse with line spacing of 328 ft. The aerial survey took place over 3 days in July 2017.
Feasibility modeling using Castile formation cave systems reveals detectability of single caves larger than 10 m diameter with FTG, however networks of smaller caves are also detectable. Polygons created from analysis of negative vertical gravity tensor (Tzz) anomalies separate the cave systems into tiered risk areas.
Initial analysis reveals risk at both pads where losses occurred. Extending the analysis to the entire survey, the drilling events in the drilled offset wells match with the risk interpreted for karst. FTG data and subsequent interpretation offer strong correlation to known shallow hazards and cave systems, making it a useful tool for risk assessment. It recommended to locate future drill pads in the identified moderate risk areas and that any new wells be located away from elevated risk areas.
This is the first application of FTG to classify drilling risk of karst features in the Permian basin. The FTG hazard map improves operational integrity of surface location selection and is a complement to surface topography and geology considerations. The FTG data and analysis also holds promise for fault mapping and for water drilling efforts.
Salahuddin, Andi A. B. (Abu Dhabi National Oil Company, Onshore) | Khan, Karem A. (Abu Dhabi National Oil Company, Onshore) | Al Ali, Reem H. M. (Abu Dhabi National Oil Company, Onshore) | Al Hammadi, Khaled E. (Abu Dhabi National Oil Company, Onshore)
This paper described the novel approach for stochastically modeling complex carbonate reservoir lithofacies and properties distribution within a High Resolution Sequence Stratigraphy (HRSS) framework. The carbonate lithofacies discussed in this paper contains heterogeneous pore types and properties. The reservoir displays an extensive range of geologic and petrophysical properties that make the efficient recovery of hydrocarbons is a challenging task. Hence one of the key steps in improving the recovery factor is by defining the three dimensional variability patterns in the reservoir in the form of fine geocellular static model. The key static geological elements that must be well defined are HRSS framework, lithofacies architecture, and field wide rock properties.
Subsurface analysis was done by examining 600 feet core footage from more than 15 wells, conventional logs from more than 50 wells, and more than 350 thin sections. The reservoir section averages 35 feet that can be subdivided into 6 high-frequency sequences. The reservoir consists of lagoonal packstone-rudstone, grain rich ooid-peloid shoal, and rudstone-boundstone mid-ramp. The shoal deposits exhibit the best permeability and oil saturation and it consists of discontinuous lithofacies body that depicts locally excellent porosity and permeability characteristics.
Lithofacies geometry and properties studies must form a fundamental basis for characterizing and modeling HRSS framework and lithofacies architecture variability through the reservoir. Combined with wireline-log data, they provide a basis for defining both reservoir framework and rock attribute distributions.
Complex lithofacies geometries and transitions, both vertically and laterally between the mound and discontinuous grain-rich ooid-peloid shoal lithofacies together with the continuous and sequential lagoonal and mid-ramp lithofacies does not allow to simulate these sorts of lithofacies assemblage using single lithofacies model algorithm. Hence a new holistic approach was implemented. A combination of Object Based (OB) algorithm and Truncated Gaussian Simulation (TGS) algorithm was employed to handle the complex lithofacies transition. This enables generating multiple realistic field wide lithofacies distribution and relationship which aligns with data trend, subsurface analog in the nearby fields, as well as that is from the outcrop exposure. The established lithofacies distribution within HRSS framework was then used to constrain field-wide properties and diagenetic trend and distribution in the reservoir.
This new holistic approach has recently been successfully implemented in the studied field. The resulted geostatistical model was able to explain pressure depletion and production rate as shown in historical production data of the field. The resulting dynamic model will hence provide reliable production forecast and reservoirs development plan which will eventually allow accomplishing the mandate recovery target.
Each basin has its own geophysical and geologic challenges that we need to address. These will change due to the geology and depth of burial. This paper will investigate challenges in two distinctly different basins. The Delaware basin in west Texas has a severe near surface problem that degrades the quality of seismic within the basin. We will investigate the use of near surface velocity model building tools to build a better understanding of the near surface geology. The Appalachian basin of southwest Pennsylvania offers a different set of challenges. In this area high values of epsilon have been observed. In this case a robust method to determine the anisotropic parameters are necessary for success. With a robust toolbox and the experience to deploy it correctly you can optimize the rate of return for your assets.
Presentation Date: Thursday, October 18, 2018
Start Time: 8:30:00 AM
Location: 204C (Anaheim Convention Center)
Presentation Type: Oral
Shallow hazards associated with dissolution karsting within the Castile formation of the Delaware basin of west Texas represent a significant drilling hazard. One operator encountered four karst related cavities within the first four hundred feet of section from two separate pad sites. The intersection of these dissolution cavities resulted in the loss of significant amounts of drilling fluids and concrete, resulting in the abandonment of the boreholes. Approximately 1100 line-km of Airborne Full Tensor Gradiometry (FTG) data are acquired at a nominal line spacing of 100 m and drape elevation at 80 m above the ground surface in order to rapidly identify and assess further risks to drilling in the adjacent lease acreage. 2.75D and 3D models are constructed to determine detectability and identify relevant wavelength and amplitudes based upon information collected from the karst cavities. Focused enhancements of the acquired data reveal correlation to the drilled cavities, but the wavelengths are too broad to assess drilling risks. Curvature analysis of the FTG data reveal a striking correlation to cavern analysis performed in outcropping areas of the Castile formation. Riskiest and safest drilling sites are identified by means of analyzing the curvature information.
Presentation Date: Tuesday, October 16, 2018
Start Time: 8:30:00 AM
Location: 207A (Anaheim Convention Center)
Presentation Type: Oral
Minimizing the footprint of marine operations in the O&G sector is of uttermost importance to ensure business sustainability. Oil spills due to a number of activities and hazards are one of the major concerns offshore. Risk assessments must carefully cover all possible control and recovery barriers and the appropriate response resources must be kept on guard against any event. The likelihood, consequences and vulnerability of the affected area shape the risk in any possible oil spill. Spillage rate and time of release depicture to a great extent the consequences of the spill, thus an early detection is crucial to minimize impact as well as to help reduce reaction time and resources scale for the responders.
An early detection tool was satisfactorily put in place either in offshore production rig and maritime terminal, with specific capabilities for automated (unmanned) detection, 24/7 recording, remote surveillance, alarm logging and very low threshold detection level in adverse weather conditions. This means a digital transformation in the surveillance of marine operations allowing the exploitation of data to get the information needed to improve Safety in operations. With a threefold approach for innovative environmental protection, asset risk/integrity assessment and transparency culture promotion, a detection system was co-developed by operator and vendor to meet assets and operations needs and produce a tailor-made product. Such a novel system combines wide-coverage radars together with high-precision infrared cameras commanded and integrated by intelligent algorithms. Lessons learnt out of event reporting from this tool will be shared to help reinforce the link between prevention and response policies and protocols.
Key tactical information for quick response, resources optimization, routine/critical operations monitoring, and real-time data sharing either internally or with third parties is yielded out of the System (HEADS) as a new input for a holistic and proactive approach towards asset protection.
Willis, John (Occidental Oil & Gas Corp.) | Tellez, Diego (Occidental Oil & Gas Corp.) | Neel, Randy (Occidental Oil & Gas Corp.) | Caraway, Greg (Occidental Oil & Gas Corp.) | Adam, Derek (Occidental Oil & Gas Corp.) | Rodriguez, John (Occidental Oil & Gas Corp.)
The drilling practices, well designs, and experiences from drilling 179 unconventional horizontal wells drilled from 2012 through late 2017, in the New Mexico Delaware Basin, are presented.
Geological conditions addressed include high-pressure flows, lost circulation, salt and anhydrite, and drilling effects. Successful practices covered include casing design and setting depths, bits, rotary steerable systems (RSS), rig specifications, pad layout, and others. Mud systems discussed include brine, mixed-metal hydroxide, invert and direct emulsions. The benefit of rotary steerable drilling assemblies is discussed. Techniques to predict, prevent, and mitigate the effect of downhole vibrations are addressed, including bit and bottom-hole-assembly design, and operating practices.
Overall drilling speed was increased by 149% (measured as feet-per-day) during the period from 2012 to 2017 through the practices that are covered. During the same period, average lateral lengths increased from approximately 3,000 ft in 2016 to approximately 7,000 ft in 2017, with 10,000 ft laterals common. Rig capabilities, pad layout, casing designs, drilling fluids, drilling dynamics practices, and other designs improved significantly in the past 3 years. A methodical approach to vibrations has proven to be critical to consistent performance. Direct emulsion mud has shown promising results as a low-density fluid with salt-saturated water phase. Casing designs were optimized to eliminate strings in some cases, and to reduce hole sizes in other cases. Rig modifications were required to support long laterals and larger drill pipe sizes.
The economic success of New Mexico unconventional developments is heavily dependent on minimizing well cost. It is a difficult area requiring complex optimization.