Noguera, Ivan Lanusse (YPF) | Fantin, Manuel (Chevron) | Crespo, Pablo A. (Chevron) | Crousse, Luisa (Chevron) | Reijenstein, Hernan (Chevron) | Varela, Raul (YPF) | Bonelli, Andres (Chevron) | Morales, Fidel (Chevron)
Vaca Muerta Formation is very well known to be one of the most promising shale oil and gas emerging plays in the whole world. Petrophysical properties make this formation very attractive, however geomechanical characterization is critical due to the high pore pressure and stress relationship that tends to generate sub-optimal vertical fracture growth. The substantial thickness (50 to 450 meters) of Vaca Muerta play and lateral/vertical heterogeneity creates a big challenge for even the most specialized people when selecting the best place where to land a horizontal well.
Narambuena field is an exploratory block located in the Northern region of Neuquén Basin within the oil window (API 32° – 42°). A multi-disciplinary team carefully designed a data acquisition plan to optimize the value of information and achieve the best landing point decision. In order to delineate the play in this block, 3 vertical wells were drilled and completed. Decisions were made using full suites of logs for petrophysical and geomechanical evaluations, rock characterization (from cuttings, sidewall cores and core), fluid characterization, frac height analysis and production logging to identify the best performing zones. In order to evaluate horizontal well production performance for future development scenarios, a horizontal well was drilled and completed. An additional vertical well was executed in a lower maturity edge of the block to better characterize the size of the opportunity. This document describes the data acquisition plan and the decision process to successfully execute the delineation plan of this field.
For unconventional plays the landing point definition of a horizontal well is critical to be taken by a subsurface team in order to improve the ultimate recovery factor of the well. Defining the right position depends on both the reservoir properties behind the wellbore and the frac efficiency of the stimulated zone.
The focus of this work has been the characterization of Vaca Muerta Formation as a shale reservoir in order to define the proper landing interval of the first horizontal well in Narambuena area. This early Tithonian to early Valanginian marine succession of siliciclastic to calcareous mudstones, first defined by Weaver (1931) as Vaca Muerta Formation, is the main source rock of the Neuquen Basin, which in the last 7 years has become a main target for the exploration and delineation of shale gas and oil.
Mukhametova, N. (Oil and petrochemical refining institute) | Kolchin, A. (Ufa State Petroleum Technology University) | Elizarieva, N. (Ufa State Petroleum Technology University) | Akhtyamov, A. (Ufa State Petroleum Technology University) | Ovechnikov, A. (NPO "InTech") | Kurochkin, A. (NPO "InTech")
The objective of the work is to develop technical measures for the reconstruction of a major gas condensate field processing facilities - central processing plant of Valanginian horizon raw gas of the Vostochno-Urengoyskoe gas condensate field (design pressure - 6.0 MPa), and the assessment of the impact of these measures on the economic efficiency of the plant. Developed technical measures require minimal investment and include application of fractionation technology by means of available energy flows at an intermediate separation stage as well as at gas condensate stabilization, optimization of piping arrangement scheme, recycling of unstable condensate weathering gas. The implementation of these measures allows: to improve the separation degree of light and heavy gas components (improves the quality and yield of commercial gas and increases the yield of stable gas condensate), to ensure the recovery of the cold reduced condensate (reduces the temperature at the stage of the low-temperature separation), to reduce the pressure loss during preliminary raw gas treatment (which increases feasible pressure drop at the low-temperature separation stage) and decrease the amount of gas flared (increases yield of commercial gas).
Reservoir characterization and modelling of highly heterogeneous carbonate reservoirs encompasses the interplay between petrophysical properties, facies, diagenesis, and their relationship with depositional environments. This case study describe a strongly dolomitized carbonate reservoir of Valanginian age onshore Kazakhstan, Central Asia. A reservoir model was built by using an integrated workflow with all the available data, namely seismic, cores, thin sections, logs and MICP. In order to build a robust subsurface model and reduce uncertainties, reservoir rock types (RRTs) were defined and modelled honouring depositional trends and diagenetic attributes.
Due to the complexity of the reservoir, the Winland R35 method, together with Lorenz plots and petrophysical groups, was used to derive the RRTs and to assign a porosity-permeability relationship for each RRT. The uncertainty in the reservoir property models was evaluated with different RRT connectivity scenarios, driven by depositional and diagenetic concepts.
With the integration of diagenetic trends in the model, it was possible to capture the heterogeneity of the reservoir and better understand the porosity and permeability distributions. This has led to development plan optimization through the definition of sweet spot areas and an improved STOIIP calculation.
The results indicate that a substantial improvement in reservoir understanding can be achieved with an integrated reservoir characterization and modelling process that accounts for depositional and diagenetic trends, especially in reducing subsurface uncertainty. Furthermore, it was possible to recognize spatial trends and capture the relationship between petrophysical properties, pore architecture and sweep efficiency. It is expected that the ultimate recovery will also improve.
The case study field is located onshore Kazakhstan, and comprises several oil bearing units. The principal reservoir corresponds to Aptian deltaic-marine sands, whereas this study addresses a secondary reservoir, which is the Valanginian carbonate. The producing structure is an E-W oriented anticline with a western downdip, where some faults are present.
The Carbonate reservoir was discovered as an upside in the mid-2000’s while drilling an exploration well. Encouraging flow tests from a 6 m interval have led to the kick-off of a detailed reservoir modelling exercise, in order to support a development plan. After that, a first pass static model was done with just a few wells. More recently, several appraisal wells were drilled to delineate the extent of the Carbonate reservoir.
The Valanginian Carbonate comprises fine grained limestone, dolomite and marl. This total interval is some 370-400 m thick (Figure 1). The oil bearing unit itself occurs in the uppermost part of the interval, and is mainly composed of skeletal dolopackstone, dolowackestone/dolopackstone, doloboundstones, with some intervals of dolomudstones. This oil bearing unit presents layer cake geometry, and is sealed by anhydrite.
Its geological and petrophysical variations are significantly linked to the geodynamic history of the basin strongly related to the transition from extensional reactivation to thermal relaxation which characterized basin s evolution through time. Major cyclic events related to sea oscillations provided the proper marine environment conditions to promote the development of several source rocks within the basin apart from Vaca Muerta Formation, such as Los Molles and Agrio formations. Regional surface data suggests that vertically (time domain) and laterally (space domain) Vaca Muerta Formation comprises a wide variety of lithologies: shales, marls, carbonates, calcareous sandstones and sandstones. Subsurface data, obtained from mud logging, cores and open hole logs also demonstrate it. Both sources provide sufficient sampling density for interpreting the different facies of the unit from the Lower Tithonian to the Lower Valanginian and also considering its areal extent within the basin. These variations are related to the basement fabric, post-rift subsidence interrupted by inverse reactivation, east-west basin asymmetry and climate changes from semiarid seasonally humid to warm and dry. A summary of these characteristics are: a) a prograding NW carbonatic ramp best represents depositional environment; b) formation thickness increases to the west and north; c) carbonates are better developed in proximal areas; d) organic matter content increases at the base of the formation; e) paleotopography clearly controls facies distribution; f) to the north of the basin hydrocarbons are related to organic rich argillaceous limestones, to the center of the basin are mostly pelithic sediments while to NE correspond to a mixture of the above mentioned, to the south the euxinic conditions favored hydrocarbons with increased sulfur concentration. Consequently these vertical and lateral facies variations control key aspects such as: areal distribution, depth, thickness, porosity, permeability, heterogeneity, TOC, mineral composition, reservoir pressure and geomechanics. In this paper a comprehensive analysis using outcrop, well, and laboratory data of the Vaca Muerta Formation are presented summarizing the main hydrocarbon s accumulations with its unconventional reservoir characteristics.
Bockstedt, a mature oilfield in Northern Germany, was discovered in 1954 and put on-stream in the same year. The waterflooding of this high permeability Valanginian sandstone reservoir, with moderately viscous oil and highly saline brine was started in 1959 and continues to date, albeit at a high watercut. A compartment within this field was selected for a pilot test of the biopolymer Schizophyllan; a polysaccharide, with considerable viscosifying efficiency and high salinity and temperature stability.
As the biopolymer flood progresses, surveillance and monitoring techniques that estimate in-situ polymer properties and help to understand the influence of the polymer on reservoir performance are applied. Operational procedures have also been developed and tested to ensure a manageable restart of operations in the event of planned and unplanned well shut-ins. Production logging test runs in the injection well during the water injection phase showed a homogeneous injection profile over the reservoir interval. Well logs from new wells drilled within the pilot area provide additional insight with regards to the saturation distribution. Passive and partitioning tracers have been injected and are regularly being sampled and analysed.
After a successful polymer injectivity field test was conducted in mid-December 2012 for Schizophyllan, continuous polymer injection commenced in early January 2013. High-resolution data available from permanent downhole gauges show an initial increase and subsequent stabilization of bottom-hole pressure at a higher value in the injection well after the start polymer injection. A modified Hall plot used to assess the polymer injectivity does not show any significant reduction in injectivity. An estimation of the reservoir properties during the water injection phase and subsequently the in-situ effective polymer viscosity during the polymer injection phase using several falloff tests confirms that, the polymer is not shear degraded in the reservoir and offers insight as to the position of the polymer front in the reservoir. The work was accompanied by numerical simulation to better understand the in-situ rheological properties of the polymer.
This paper discusses the challenges, experiences and early results from the operational aspects of an on-going polymer flood pilot in a mature oilfield after an early technical evaluation.
Carbonate reservoirs are commonly heterogeneous and their reservoir quality results from complex interactions between depositional facies and diagenetic processes. The Diagenetic Diagram is a powerful tool that helps in the characterization of the diagenetic processes that have affected the reservoir. From this knowledge, it is possible to significantly improve the understanding of the reservoir's pore system and permeability distributions, which are key factors for development optimization and production sustainability.
A multi-scale and multi-method study (petrography, blue-dye impregnation, selective staining and porosity determination) of Middle Jurassic carbonates from the Lusitanian Basin (Portugal) has been undertaken, to find the best systematic approach to these reservoirs. It has involved thorough diagenetic characterization of each lithotype (lithofacies, texture, porosity, qualitative permeability assessment and diagenetic evolution). The study area was selected based on its excellent and varied exposures of carbonate facies and availability of core.
Methodological and terminological challenges were faced during the study, especially dealing with data coming from several scales (macro, meso, and micro). In order to overcome these challenges, a diagenetic diagram was developed and applied to the selected rocks. It is a tool that allows the integration of data coming from outcrops, hand samples, cores, cuttings, thin sections, and laboratory experiments.
This is carried out in a dynamic, guided, systematic, and rigorous way, enabling the evaluation of the relationship between facies, diagenetic evolution and pore systems. The latter are characterized regarding size, geometry, distribution, and connectivity. This enables the identification and characterization of permeability heterogeneities in the rocks. It was concluded that the main porosity class (i.e. secondary) was created by diagenetic processes.
The proposed method has strong application potential for: detailed characterization and understanding of porosity and permeability in carbonate reservoirs, from a diagenetic evolution and fluid flow perspective (e.g. SCAL and pore system description); definition of diagenetic trends for modeling petrophysical properties and rock types. In this regard, the method is being applied to a Valanginian carbonate reservoir in Kazakhstan, and some preliminary results are presented in this paper. Refining this technique may be helpful for similar carbonate studies, enhancing the results of typical diagenetic studies by improving the characterization of reservoir properties at various scales, thus contributing to a more sustainable exploitation of hydrocarbon reservoirs.
Section 11813, Paper 1 THE WEALDEN FORMATION IN THE NETHERLANDS BY G. C. L. SUNG (*) SYNOPSIS. Beds of two entirely different facies types in the Netherlands are considered as being of the same age as the Wealden formation of S. E. England. Firstly, typical lacustrine sedi- ments occurring in the N. E. Netherland, which lithologically and palaeontologically (based mainly on the ostracod-fauna) can be correlated with the German '' Wealden " of the N. W. German basin as well as with the beds outcropping in the type locality of the Wealden in S. E. England (see correlation in Fig. I). Secondly, fluviatile-deltaic deposits occurring in S. W. Netherlands, which must be attributed, at least in part, to the Wealden formation, deduced from their stratigraphic position. No diagnostic macro- or micro-fauna has been found in these deltaic beds, so that there is as yet no definite paleontological evidence for the assumption that these beds are equivalent in age to the Wealden formation of S. E. England. Lithologicall?] the beds resemble the ferruginous deposits at Shotover Hill (Oxford), und the Li Fuhse lavers '> in boring Thoren I (near Hanover.) The presumed extent of the lacustrine Sediments in the N. E. Netherlands and the probnble extent of the Fluvintile-Deltaic deposits in the S. W. Netherlands, based on bore-hole data, are given on the palueogeographic sketch-map (Fig. 2). The position and direction is also given of the '' Nether- lands Ridge ", which influenced the sedimentation pattern in the Netherlands from late Palaeozoic to Cretaceous times. RÉSUMÉ. En Hollande, deux unités lithologiques distinctes de faciès complètement différent, ont été considérées comme appartenant au même âge que la formation du Wealdien du sud-est de l'Angleterre. La première unité est formée par des sédiments lacustres typiques présents dans la Hollande nord-orientale, lesquels lithologiquement et paléontologiquement (surtout d'après la faune d' Ostracodes) peuvent être corrélés avec le Wealdien allemand du bassin de l'Allemagne nord-occidentale aussi bien qu'avec les afleurements de la localité type de Wealdien en Angleterre sud-orientale. (Voir la corrélation à la Fig. 1). La seconde unité résulte de dépôts fluviatiles-deltaiques présents en la Hollande sud-occi- dentale, qui, au moins partiellement, peuvent être attribués, pour leur position stratigraphique, à la for- mation Wealdien. Dans ces dépôts deltazques nn n'a pas retrouvé de macrofaunes ou de microfaunes signi- ficatives, de sorte que pour le moment il n'y a pas de preuve paléontologique définitive que ces dépôts d'un uge équivalent à celui de la formation Wealdien de l'Angleterre sud-orientale. Les couches sont litho- logiquement semblables aux dépots ferrugineux de Shot over Hull (Oxford), et aux U couches de Fuhse )) dans le puits Thoren I, près de Hannovre. L'extension présumée des sédiments lacustres en la Hollande n