Africa (Sub-Sahara) Gas was discovered at two separate levels in the Mronge-1 well in Block 2 offshore Tanzania. The discovery is estimated at between 2 and 3 Tcf of natural gas in place, bringing Block 2's estimated total in-place volumes up to 17 to 20 Tcf. Statoil (65%) operates the Block 2 license on behalf of Tanzania Petroleum Development Corporation, and partners with ExxonMobil Exploration and Production Tanzania (35%). Oil was discovered at the Agete-1 exploration well on Block 13T in northern Kenya. The well, drilled to a total depth of 1929 m, encountered 330 ft of net oil pay in good-quality sandstone reservoirs. Tullow Oil (50%) is the operator with partner Africa Oil (50%). Asia Pacific Indonesia announced plans to offer 27 oil and gas blocks in 2014 in regular tenders and direct offers.
Africa (Sub-Sahara) A drillstem test was performed on the Zafarani-2 well--located about 80 km offshore southern Tanzania. Two separate intervals were tested, and the well flowed at a maximum of 66 MMscf/D of gas. Statoil (65%) is the operator, on behalf of Tanzania Petroleum Development Corporation, with partner ExxonMobil Exploration and Production Tanzania (35%). The FA-1 well--located in 600 m of water in the Foum Assaka license area offshore Morocco--was spudded. The well targets Eagle prospect Lower Cretaceous resources. Target depth is 4000 m. Kosmos Energy (29.9%) is the operator, with partners BP (26.4%),
Africa (Sub-Sahara) Eni discovered gas and condensate in the Nkala Marine prospect offshore Congo. The discovery could hold from 250 MMBOE to 350 million MMBOE in place, the company said. In a production test, the Nkala Marine 1 discovery well in the Marine XII block yielded more than 10 MMcf/D of gas and condensate. Eni is the operator with a 65% interest in the block. The remaining shares are held by New Age (25%) and Societé Nationale des Pétroles du Congo (SNPC) (10%). Sonangol and Total will break ground on a deepwater oil pumping project that will increase Angola's production by more than 30,000 B/D.
Africa (Sub-Sahara) Eni has begun production from the Vandumbu field and made a new oil discovery in the Afoxé exploration prospect in Block 15/06 offshore Angola. First oil from the Vandumbu field, through the N'Goma floating production, storage, and offloading vessel, was achieved in late November, 3 months ahead of schedule. Vandumbu is approximately 350 km northwest of Luanda and 130 km west of Soyo. This, along with the startup of a subsea multiphase boosting system in early December, boosts oil production from Block 15/06 by 20,000 B/D. The rampup of Vandumbu is expected to be completed in 1Q 2019. Block 15/06 is being developed by a joint venture formed by Eni (36.84%, operator), Sonangol (36.84%), and SSI Fifteen (26.32%). Asia Pacific Ophir Energy's Paus Biru-1 exploration well in the Sampang production-sharing contract (PSC) offshore Indonesia has resulted in a gas discovery.
Contretras et al. (2005) briefly mentioned time alignment of partial-angle stacks for correction of residual NMO, and Araman et al. (2014) talked about evaluating the overall quality of the pre-stack gather flatness via estimates of gross time misalignment between angle stacks. Angle stack similarity QC Evaluation of pre-stack data consistency, as proposed by Paternoster et al. (2009), can be performed by crosscorrelating pairs of sub-stacks at a finer sampling rate across a long enough time interval. In addition, Coleous et al. (2013) and Araman et al. (2014) both pointed out that correlation between angle stacks over an objective-defined window (e.g. at the key horizon or reservoir level) is a commonly used and quantitative QC method for AVA/AVO or seismic inversion studies. When near-and far-angle stacks are cross-correlated, areas where seismic events line up nearly perfectly with minimum or no shifts between the angle stacks would have zero or nearly zero lag times on the cross-correlation calculation. High cross-correlation peak lag times would be indicative of misfit in seismic events between the angle stacks, and this would represent non-flatness of seismic gathers and hence a non-optimal velocity model. Thus, this is the basis for using the cross-correlation as a global QC of optimal velocity model or image-focusing quality.
… And expecting different results. Electrical heating of oil reservoirs has fascinated petroleum engineers for more than 70 years - longer, if you include the use of heaters in Siberian oilfields. The earliest laboratory study was done in Pennsylvania in 1940's. Since then, many more studies and field tests have been carried out, none of which was a commercial success. This paper takes a look at different forms of electrical heating, the supporting theoretical work, and field tests. Additionally, several examples are given illustrating the limitations of electrical heating processes. Also discussed is the logic behind the resurgence of electrical heating in recent years. Not discussed are over 200 patents on electrical heating. The major electrical heating processes are resistance heating, using direct current or low frequency alternating current, induction heating, microwave heating, and heating by means of electrical heaters. These are described briefly, and compared. In applications to oil sands, the intent is to utilize the connate water as the heating element (resistance heating) or oil sands as the dielectric (microwave heating). Induction heating is much less effective but has been tested in many field projects. Shale that has a permeability of zero to fluid flow, is electrically conductive, and thus channels much of the electric current flow in resistance heating, which also has other limitations. Microwaves suffer from low depth of penetration (of the order of 20 cm in oil sands) and low power delivery (of the order of 1 MW as a maximum). The power requirements for a typical SAGD pair, in contrast, are 15-30 MW. Electric heaters have been used in oilfields for many years for near-wellbore heating. Two large field pilots used powerful electric heaters, and were recently shut down. Although electrical heating has not had commercial success, recently there has been a resurgence in various electrical processes, as a means of reducing GHG emissions, under the flawed logic that oilfield use of electricity would displace emissions caused by steam generation.
Reservoir Mapping While Drilling tool, consisting of a Deep Directional Electromagnetic Propagation Resistivity (DDEM) Logging While Drilling (LWD) tool and associated imaging software can detect bed boundaries and map reservoir bodies laterally beyond the wellbore being drilled. It has been successfully deployed to resolve and overcome geological and reservoir uncertainties when drilling wells offshore Malaysia. In Case Study-1, the DDEM tool was used to locate and navigate the drilling borehole assembly within a turbidite target reservoir successfully. In addition, the Reservoir Mapping While Drilling tool was able to detect and map a hydrocarbon bearing sand ten metres below the original borehole. In Case Study-2, the DDEM tool was used to identify the current Gas Water Contact (GWC) in a carbonate field which was experiencing high water cut early in the life of the field. In Case Study-3, the DDEM tool was used to determine the Top of Carbonate (TOC) in a carbonate gas field. It was critical that the top of carbonate be identified correctly, as the surface seismic data was relatively poor and was not able to pinpoint the TOC accurately. In the first case study, the hydrocarbon pay sand would have been completely missed if standard LWD tools alone were used to drill the well in a mature field. In the second case, the DDEM tool was able to locate and map the current Gas Water Contact (GWC), which was found 35 metres below the wellbore, in the carbonate gas field. It was found that the water was being produced through a karst zone, although all the previous production wells had been drilled horizontally way above the original GWC. In the third case, the DDEM tool was able to detect the Top of Carbonate, thereby allowing to set the casing shoe above the TOC. The plan was to set the intermediate casing shoe just a few metres above the TOC to avoid encountering severe mud losses when drilling through the carbonate reservoir. This paper will discuss the various steps involved in planning, designing and drilling of these wells using the DDEM tool with the associated reservoir mapping software. The methods used in imaging the reservoirs of interest and the bed boundaries and results obtained will also be discussed.
Lima, C. (Independent Researcher) | Lavorante, L. P. (Independent Researcher) | Williams, W. C. (Louisiana State University) | Beisl, C. (UFRJ-COPPE) | Reis, A. F. C. (Petrobras) | Carvalho, L. G. (Petrobras) | Moriss, M. (Paradigm)
ABSTRACT: This study proposes that a systematic comparison using integrated 3D visualization of all pertinent data (midplate seismicity, geological and geophysical variables) could help in identifying areas vulnerable to injection-induced seismicity in the North American plate. From similar studies of the South American plate in Brazil’s Potiguar basin, it is found that intraplate seismicity occurs at uplifted basin borders (areas over thin, hot, weaker lithosphere) where pre-existing faults are prone to be reactivated by small pressure perturbations. Conversely, central basins (areas over thick, cold, strong lithosphere) are not prone to seismicity. With this model we investigate Oklahoma (Ok) and North Dakota (ND), both intense areas of injection. ND activity, in the central basin, shows no induced seismicity. In contrast, Ok activity, in a regional-scale ravine in the uplifted basin border, has seen a 62.5-fold increase in recent seismicity. Modeling of the Ok region shows reactivation of pre-existing faults with injection pressures of 1.75 MPa (254 psi; 0.7ppg) between 2000-2200m depths, values that agree with wellhead injection pressure field data.
1. INTRODUCTION: THE PROBLEM
A huge increase of seismicity in the tectonically stable U.S. is put into evidence, if we examine the USGS Catalog, 2017 comparing the number of earthquakes of magnitude (Mw) greater or equal to 4 that occurred during 2000-2010 and 2010-2016. For this area, see Fig. 1, we jumped from an average of 6.2 events/yr, during 2000-2010, to an average of 28.8 events/yr, during 2010-2016, roughly a 5-fold increase. For Oklahoma, see Fig. 2, a 62.5-fold increase of seismicity has been observed when comparing these same two periods, including two major events (Mw 5.7, 2011; Mw 5.8, 2016). These recent increases are contemporaneous with the increase in shale production as shown in Figs. 1 and 2. In the stable midcontinent, a roughly 5-fold increase is observed in seismicity during 2010-2016. Again, the increase is contemporaneous with US shale production.
Jiang, Ming (China University of Petroleum) | Ke, Shizhen (China University of Petroleum) | Kang, Zhengming (China University of Petroleum) | Sun, Xu (China University of Petroleum) | Yin, Chengfang (China University of Petroleum)
Identifying low-resistivity reservoirs, which are important oil reservoirs with considerable productivity, is a real challenge to conventional electrical resistivity logging methods. For this reason, this paper introduces a new spectrum logging method for effective identification of low-resistivity reservoirs. This method measures the complex-resistivity spectrum of formation, which is sensitive to water-filled porosity without the influence of low resistivity. This paper presents the relationships between the complex-resistivity spectrum and petrophysical properties based on laboratory data. The electrode array of the prototype for borehole testing is also described. A numerical simulation was performed to study the detection characteristics of this prototype and field tests were conducted to verify the feasibility of this method. The results show that variations in water-filled porosity obtained by this method show a good fit with the actual values. Further, water saturation can be obtained for oil reservoirs, especially for low-resistivity reservoirs. This logging method provides an approach to characterize oil reservoirs that is more effective than existing methods for the case of low-resistivity reservoirs.
During the past four decades, an increasing number of low-resistivity reservoirs have been discovered in new locations. Today there are many documented records of low-resistivity reservoirs in locations including the Gulf of Mexico, North Sea, Indonesia, Venezuela, and the Tarim Basin. Several studies have proven the productivity of these reservoirs (Zemanek, 1989; Souvick, 2003), but the term ‘low-resistivity reservoir’ is rather relative and lacks an absolute description. Low-resistivity reservoirs not only imply low absolute values of resistivity, but also a lack of positive contrast in measured resistivity between the reservoir and the water zone, making them difficult to identify using traditional electrical logging data. There are many causes of low-resistivity reservoirs, but there is usually only one primary cause in any given location. For example, Gulf Coast (USA) and Misoa Sands (Venezuela) are caused by laminated shaly sand (Ruhovets, 1990; Coll et al., 1996), Midway Sunset Field (California, USA) and Potiguar Basin (NE Brazil) are caused by fresh formation waters (Wharton et al., 1981; Condessa, 1995), and the Simpson Series (Oklahoma, USA) is caused by conductive minerals (Schulze et al., 1985).
Beyond offshore West Africa where modern densely-sampled data from ships and satellites have played a key role in current understanding of passive margin evolution, Africa is in general rather unevenly known, especially in the subsurface in more remote areas. The GIS-based Exploration Fabric of Africa (EFA, the ‘Purdy project’) was designed to address that problem. It includes structural features such as faults and basin outlines but at a very high and often generalized level, divorced from their underlying genetic linkages. We have undertaken to compile a more detailed tectonic synthesis aimed to integrate understanding of the oceanic margins with the continental realm. This is an overlay to EFA with a variety of public domain, published, non-exclusive, and derivatives of proprietary work at a closer and more detailed level, importantly guided by known patterns of structural styles. Potential field (gravity and magnetic) data provide guidance in locating, extending, and connecting key mapped features; we then rely on the kinematic patterns to predict missing details in a testable interpretation. The result is a detailed structural features map that can function as a framework within which to target and prioritize both conventional and unconventional activity by operators and licensing/regulatory organizations. We illustrate the process in theory and in practice along the Central African Rift System (CARS), where data is sparse. This fault linkage systems approach has flagged underexplored areas where unmapped structure is likely that could, for example, be targeted with hi-resolution geophysical data. A similar system to CARS appears to cross southern Africa from Namibia to Tanzania - a “Southern Trans-African Rift system" or STARS. Exploration in the eastern Owambo Basin resulted in the mapping of a pull-apart basin from depth-to-basement inversion of high-resolution magnetic data and subsequently studied with structural modeling. Thinking in terms of such fault and structural systems, this ‘Kavango Basin’ can be related along strike to the Karoo Basins in Eastern Africa via features such as the Omaruru lineament, implying the possibility of a fairway of extensional basins and shears across the continent that are not obvious in existing low-resolution data. STARS represents a blue-sky frontier concept for both conventional and nonconventional exploration potentially offering new exploration leads, the ultimate objective of big picture work.