Organic-rich mudrocks (ORM) from the Brushy Canyon Formation in west Texas were deposited in the Middle Permian during the Guadalupian epoch in the Delaware Basin. Brushy Canyon ORM were examined for Re-Os isotope systematics with a goal of constraining their depositional age, the 187Os/188Os value of seawater at their time of deposition, and to examine how Re and Os partition into organic material in ORM. For these samples, Rock-Eval pyrolysis data (HI: 228-393 mg/g; OI: 16-51 mg/g) indicates predominantly Type II marine kerogen with minor contributions of Type III terrestrial organic matter. Rhenium and osmium abundances correlate positively with HI, and negatively with OI, which are proxies for organic matter type and degree of preservation. These data are consistent with previous work that indicates Re and Os abundances are controlled by the availability of chelating sites in the kerogen. Brushy Canyon Formation samples have (total organic carbon) TOC values between 0.97 and 4.04% and show a strong positive correlation with both Re and Os abundances, consistent with correlations between these parameters in other ORM suites. The positive slopes in these correlations are distinct between marine (higher slopes) and non-marine (lower slopes) lacustrine environments of deposition. The Brushy Canyon’s steep slopes are consistent with marine deposition of its organic matter and an open-ocean non-restricted setting. The relationship to other Re-Os and TOC data sets appears to be a function of the restrictivity of marine conditions, and associated variations in reducing conditions during ORM accumulation of the Delaware Basin compared with more restricted lacustrine basins with local drawdown of Re and Os.
The Re-Os isotope systematics of ORM from the Brushy Canyon Formation yields a Model 1 age of 261.3 ± 5.3 Ma (2.0% age uncertainty; MSWD = 0.82). Within the uncertainty, this agrees with the expected Guadalupian age for this formation. This Re-Os age represents the first direct, absolute age for Guadalupian organic matter in the Delaware Basin. The initial (187Os/188Os)i = 0.50 ± 0.06 obtained by isochron regression represents the 187Os/188Os of seawater at this time. This value is significantly less radiogenic than modern day seawater (~1.06). The lower 187Os/188Os of Guadalupian seawater recorded is likely caused by a decrease in the relative flux of radiogenic Os from continental weathering due to a number of local and global climatic and tectonic changes that were occurring during this time.
Pendkar, Narender (PETRONAS Carigali Sdn. Bhd.) | Rubino, Jean-Loup (Total) | Jean-Baptiste Baby, Guillaume (U. of Rennes) | Sia, Simon Seak Lung (PETRONAS Carigali Sdn. Bhd.) | Prasetyotomo, Wahyu Singgih (PETRONAS Carigali Sdn. Bhd.)
This paper reports observations carried out on Carboniferous to Permian sedimentary rocks in Moatize Basin in Tete Province. The outcrops of Vuzi, Moatize and Matinde Formations ranging in age from Late Carboniferous to Late Permian were logged and sampled along river sections. The Vuzi Formation is made up of diamictites with thin bedded sandstone intercalations, laminated shale and localized hemispheroidal stromatolitic limestone which were deposited in glacio-fluvial to lacustrine depositional systems. The stromatolitic and laminated limestone was formed during a deglaciation episode on the lacustrine margin. The younger outcrops of Moatize Formation are characterized by thick stacked braided and meandering fluvial, and lacustrine deposits with intervening coal seams. The lacustrine deposits are characterized by fissile shales with thin, laterally persistent fine grained sandstones and siltstones. The lacustrine depositional systems range from shallow, with localized deposits of several meters of laminated grey silty shales within the confines of fluvial deposits, to deep, with a thickness of tens of meters having dark grey shale associated with rhythmic turbidites.
The spate of hydrocarbon discoveries in Rovuma Basin, Mozambique during the recent years (Fruhauf, 2014) have paved way for an outline of petroleum systems. While the role of Tertiary and Mesozoic geological elements are well understood (Salman and Abdula, 1995), the stratigraphic and tectonic framework of deeper Karoo sedimentary sequences has not been completely deciphered (Figure 1). The regional sequence stratigraphic analysis studies carried out by Sapri et al. (2013) in southern part of Rovuma basin has established up to five sequences from Triassic to the Present. With absence of well data, the characteristics of the deeper Karoo sedimentaries could not be recognized with confidence based on seismic data alone. The objectives of the study are to use outcrops as analogues for understanding sedimentological and source rock characteristics for the deeper part of rifted sedimentary sequence within the offshore Rovuma Basin.
The Karoo sedimentation in various south and central African basins has been extensively documented (Cairncross, 2001; Catuneanu et al., 2005). For this study, Moatize Basin was chosen as it offers excellent outcrops of sedimentary rocks deposited in a rift sequence ranging in age from Late Carboniferous to Late Permian, making it an ideal analogue for understanding sedimentological and source rock characteristics for the deeper part of rifted sedimentary sequence within the offshore basins like Rovuma, the site for recent prolific hydrocarbon discoveries on the eastern margin of Africa. In addition to the coal bearing outcrops of the Permian encountered along the Muaradzi and Moatize river sections, the Vuzi Formation, the equivalent of the Dwyka Tillite was also examined along the Murongozi river section (GTKa, 2006).
The geology of the Tete Province is structurally dictated by the regional Zambezi Rift, which trends E-W from the Zambia-Zimbabwe border, then swings SE to S-SE through Tete. The rift was formed in Proterozoic basement rocks, developing into a zone of active extensional tectonism and sedimentary deposition. The Proterozoic basement comprises of igneous, crystalline rocks, schists and metasediments (GTKa 2006). The geological structure in the Moatize Basin is dominated by a series of high angle faults, which divide the basin (Vasconcelos, 2000).
Hydrothermal dolomitization is one of the main diagenetic processes potentially affecting the petrophysical characteristics of carbonate reservoir rocks. It's effect on Barremian lacustrine carbonates of Upper and Lower Toca Formations has been investigated through an integrated diagenetic study and simulated through a quantitative diagenetic modeling (RTM TOUGHREACT software), in order to understand the behavior of dolomitizating fluids in the carbonate reservoir rock. This approach is also useful in carbonate marine contexts. Among the analyzed core samples, the best reservoir facies are represented by coarse Mollusk Coquina limestone and hydrothermal dolomite, which is the subject of this study. Two types of dolomite have been recognized. A finely crystalline, likely early diagenetic dolomite, shows low reservoir properties, and a coarsely crystalline, likely late diagenetic zebra dolomite, with very good reservoir properties. Dolomitisation is associated with strong silica precipitation in the Upper Toca Formation, pointed out by mineralogical and chemical analyses that also document, the presence of detrital palygorskite, typical of lacustrine environments under arid conditions and, in the Lower Toca Formation, of talc replacing ooids and indicating strong hydrothermal conditions. The integration of different investigation techniques allowed to hypothesize a mechanism of dolomitization by hypersaline fluids probably mixed with modified hypersaline and fresh waters, interacting with crustal rocks, as pointed out by Strontium isotope analysis. High homogenization temperatures registered in fluid inclusions (100 to 140 C) could be due to crustal thinning, while the hypersaline fluids (20 to 25 NaCl eq.
The Oudeh Shiranish reservoir in Syria contains 5.1 billion bbls of 12-16 oAPI crude oil. However primary recovery factor is estimated to be only 5 to 7% of the original oil in place. To increase oil recovery, waterflood, VAPEX, microbial treatment and cyclic steam stimulation (CSS) were examined. Eventually, CSS was selected for a pilot test despite the depth of the reservoir, approximately 1600 meters, was deeper than most successful CSS projects in the world.
The CSS pilot was implemented in September 2006 and suspended in November 2009. The project expanded from 2 to 24 wells. Low steam quality at the bottom of the well proved to be the most prominent challenge due to a combination of heat loss in the wellbore and relatively low steam injectivity. Only hot water reached the bottomhole when steam was injected through casing. Injection into tubing improved steam quality. Vacuum insulated tubing (VIT) produced the best, increasing steam quality to between 20 and 40% at a wellhead steam quality of 80% and an injection rate of 200 m3 CWE/day. The high pressure required to inject into the Shiranish reservoir at close to or higher than initial reservoir pressure conditions means that the latent heat of vaporization is low, compared to the typical CSS injection pressure, resulting in a less effective heating process.
In the study, a new thermal simulation model was developed to examine history-matching parameters, match the well and pad performances and optimize operations if the pilot were to be continued. Excellent history matches were achieved. Forecast indicated that Shiranish CSS performance was positive and could increase oil recovery by up to 100% over cold production.