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Collaborating Authors
Summary. Experimental data from analyses of more than 20 recombined fluid samples show that a significant compositional gradient exists in the Anschutz Ranch East field. The gradient can be correlated as a linear function of depth. Using the correlation, an engineer can estimate compositions for any bottomhole location and then use other methods to estimate fluid properties and/or depletion performance. Introduction The Anschutz Ranch East field is located in the western Overthrust Belt along the Wyoming/Utah border (see Fig. 1). Initial surface production from the west lobe of the Anschutz Ranch East field production from the west lobe of the Anschutz Ranch East field gave the erroneous indication that this reservoir contained an oil either underlying or separate from other zones containing gas condensate-type fluids. The discovery well tested four different of perforations covering more than 600 ft [183 ml of structure in perforations covering more than 600 ft [183 ml of structure in the Nugget formation. The lower interval was initially thought to be an oil because it produced a stock-tank liquid of dark color and about 4]'API [0.82 g/cm3] gravity (specific gravity= 0.81948). Laboratory PVT studies, however, showed that all four sets of perforations were producing rich gas-condensate fluids with different perforations were producing rich gas-condensate fluids with different compositions, GOR'S, and saturation (dewpoint) pressures. These first few samples were analyzed without benefit of any geologic data regarding the relative isolation/communication of the four zones. Delineation wells showed that the structure continued above the perforated intervals in the discovery well. Assuming that the perforated intervals in the discovery well. Assuming that the reservoir was continuous, we estimated the saturation pressure near the top of the structure (by extrapolation of the available saturation pres-sure data) and found a dewpoint greater than the average reservoi pres-sure data) and found a dewpoint greater than the average reservoi pressure at that depth, which was not possible in this case because pressure at that depth, which was not possible in this case because deeper fluids were undersaturated gas condensates. It is possible for a recombined sample to have a saturation pressure greater than the reservoir pressure, but this indicates a situation in which two phases (free reservoir gas and saturated reservoir liquid) were both phases (free reservoir gas and saturated reservoir liquid) were both flowing together into the wellbore at the time the surface separator GOR was measured and separator fluid samples were collected. Recombination in these cases results in either too much solution gas (for a black oil) or too much retrograde liquid (for a gas condensate), both of which usually raise the saturation pressure. It was also determined from geologic data that we were dealing with one very thick zone rather than several isolated ones, supporting the concept of a continuous reservoir. According to the results of the PVT tests, it seemed highly unlikely that an oil leg was present. We were therefore forced to explain the problem of an apparent two-phase fluid system (extrapolated saturation pressure above reservoir pressure) located in a continuous reservoir at an elevation above a rich gas-condensate system. At this stage in the field's development, it was jointly decided between the research and producing departments to initiate a large-scale data-collection program on all future wells drilled in Anschutz Ranch East. The purpose of this program was to evaluate fluid properties from all wells and to develop an understanding of how those properties from all wells and to develop an understanding of how those properties varied with depth in this 1,800-ft [550-m] -thick reservoir. properties varied with depth in this 1,800-ft [550-m] -thick reservoir. Data Collection For the next 2 years, multiple sets of surface separator gas and liquid samples for recombination were collected from every well drilled in the Anschutz Ranch East field. These were transmitted to our research center for PVT analysis. In several cases, duplicate samples were sent to service company laboratories for corroborating analyses. The suite of information on each well, which was used for correlating purposes, was as follows.Well test information-true vertical depth (TVD) subsea, reservoir temperature, producing surface separator gas/liquid ratio (GOR), separator temperature and pressure, and stock-tank liquid gravity. Laboratory analyses-composition of separator gas and liquid samples and recombined wellstream through C6 with a lumped C7+ fraction, detailed chromatographic analysis of the C7, fraction, molecular weight and specific gravity of the lumped C7+ fraction, density of recombined fluid above the dewpoint pressure, dewpoint pressure of the recombined fluid, constant-composition volumetric expansion (CCVE) data (including retrograde liquid behavior), and variation of dewpoint pressure and CCVE with temperature for selected samples. The PVT analyses (CCVE tests) run at the research center were conducted in variable-volume visual cells similar to the ones described by Jacoby and Yarborough. Samples for chromatographic analysis were obtained with the procedures described by Yarborough and Vogel. Densities were obtained through use of high-pressure pycnometers. Replicate samples were obtained for compositional pycnometers. Replicate samples were obtained for compositional analyses as long as sufficient fluid was available in excess of that required for other tests. Compositions were determined with a dualchannel gas chromatograph that had an inlet splitter and used Chromasorb P-101 and SE-30 columns for the thermal conductivity and flame-ionization channels, respectively. Simulated true-boiling-point analyses by temperature-programmed gas chromatography (also referred to as "fingerprint" or "type" analyses) were performed on the lumped C7+ fraction with a 150-ft [46-m] capillary column. This test provided reasonable definition of individual carbon number cuts through carbon number 40. Data Correlation Compositional analyses of the fluids used in the correlational work are provided in Tables I and 2 (Table I for those analyses performed by our research center and Table 2 for those analyses provided by commercial service companies). Also included in these tables are the specific gravities and molecular weights of the lumped C7+ fractions, the GOR's corrected to a set of standard separation conditions (500 psia and 80 degrees F, 42 psia and 70 degrees F, and 12 psia and 60 degrees F [3450 kPa and 300 K, 290 kPa and 294 K, and 83 kPa psia and 60 degrees F [3450 kPa and 300 K, 290 kPa and 294 K, and 83 kPa and 289 K]), the corresponding depths from which the samples were collected. Because the production from the Anschutz Ranch East field was all from one formation (Nugget), it was considered highly probable that the hydrocarbons all came from the same source material. If so, the distribution of the heavy-component cuts within the C7+ fraction for all the sets of recombined fluids would be expected to be relatively similar (on a normalized basis). This assumption was found to be valid for west Texas oils, as reported by Chaback and Turek. SPERE P. 1025
- North America > United States > Wyoming > Uinta County (1.00)
- North America > United States > Utah > Summit County (1.00)
- North America > United States > Wyoming > Nugget Formation (0.99)
- North America > United States > Wyoming > Anschutz Ranch East Field > Nugget Formation (0.99)
This paper describes the first successful attempt on the continental shelf offshore UK to map carbon dioxide (CO2) in real time while logging during a drilling campaign in the East Irish Sea. Reservoirs in this sea's basin contain varying proportions of CO2, nitrogen (N2), and hydrogen sulfide (H2S), in addition to oil and methane. Two of these wells develop the Rhyl gas field. Downhole-fluid-analysis (DFA) technologies were deployed with a wireline-formation-testing (WFT) tool to measure CO2 content accurately downhole. The Rhyl field was discovered in 2009 and received development approval in 2012.
- Europe > United Kingdom > Irish Sea > East Irish Sea > Morecambe Bay > East Irish Sea Basin > Morecambe Bay > Block 113/27b > Rhyl Field (0.99)
- Europe > United Kingdom > Irish Sea > East Irish Sea > Morecambe Bay > East Irish Sea Basin > Morecambe Bay > Block 110/2a > Morecambe Field > North Morecambe Field (0.99)
- Europe > United Kingdom > Irish Sea > East Irish Sea > East Irish Sea Basin > Ormskirk Sandstone Formation (0.99)
- (4 more...)
Drillstem testing of low-permeability reservoirs is challenging because high-pressure drawdown around the wellbore lowers fluids below saturation pressure and creates two-phase flow into the wellbore. The fluids produced at surface no longer represent the original reservoir fluid. This paper shows the benefits of a careful methodology of data selection and equation-of-state (EOS) modeling to validate data used to characterize the reservoir fluid. There are significant technical difficulties in capturing representative fluid samples from tight formations. Attempts to flow to surface from tight formations induce a fall in pressure around the wellbore that may take the reservoir oil or gas below its saturation pressure.
- Reservoir Description and Dynamics > Formation Evaluation & Management > Drillstem/well testing (1.00)
- Reservoir Description and Dynamics > Fluid Characterization > Phase behavior and PVT measurements (1.00)
- Reservoir Description and Dynamics > Fluid Characterization > Fluid modeling, equations of state (1.00)
Abstract A method is proposed and applied to one of the fields in the South Caspian Basin that allows to reconstruct the initial state of a partially depleted gas-condensate field using a limited set of initial data and assess the prospects of its development. The method is based on numerical PVT-simulation with sequential stepwise gas saturation with equilibrium condensate to the dew point pressure that corresponds with the pressure at the gas-oil contact (GOC). The obtained composition at the GOC is then used to reproduce the variation of gas composition and condensate content with height above GOC taking gravity into account. At the final stage the obtained results are verified against well production data. PVT-modeling was based on laboratory studies of recombined gas samle. The residue C10+ was divided into two pseudo components C10+(1) and C10+(2). To adjust the model to the experimental results, the properties of C10+(1) and C10+(2), and the shift-parameter of methane (Sv) were modified. PVT-modeling allowed the following gas compositions to be calculated: โat the sampling depth and time; โat the sampling depth in the initial state; โat GOC depth in the initial state. The calculation of gas composition variation with height above GOC was performed. For each of the compositions obtained, the potential content of C5+ was calculated. From the development point of view, not only the initial state is of interest, but also the change of gas-condensate ratio (CGR) with reservoir depletion. To model this process, a constant volume depletion (CVD) experiment is generally used. The obtained dependencies allowed us to compare the results of calculations with the historical data. Actual values, on the whole, correlate well with PVT-modeling data, and values that do not fit into the general paradigm of the obtained regularities are a reason for more in-depth studies of the reasons that led to such a difference. The approach used allows to: โpartially fill the lack of research by taking into account the physical principles of reservoir formation; โbuild an initial equilibrium reservoir state taking gravity into account; โreduce the uncertainty of reservoir production data.
- Asia > Azerbaijan > Caspian Sea > South Caspian Basin > Shah Deniz PSA > Shah Deniz Field > Balakhany Formation > Fasila Suite Formation (0.99)
- Asia > Azerbaijan > Caspian Sea > South Caspian Basin > Shah Deniz PSA > Shah Deniz Field > Balakhany Formation > Balakhany VIII Interval Formation (0.99)
- Asia > Azerbaijan > Caspian Sea > Apsheron-Pribalkhan Ridge > South Caspian Basin > Azeri-Chirag-Guneshli Field > Azeri Field (0.99)
- North America > United States > West Virginia > Alexander Field (0.97)
Abstract The paper presents the results of a study to investigate the variation of gas composition and key PVT properties with depth in the Khuff carbonate reservoirs of the Ghawar field in Saudi Arabia. The study was performed as part of a larger effort to characterize the reservoir fluids for compositional simulation and development planning. Laboratory PVT reports on over twenty appraisal wells were used as a basis for the study. It was found that both condensate content and hydrocarbon compositions decreased with depth and/or temperature while acid gas composition increase with depth. The composition of hydrogen sulfide varied from zero, at a threshold depth and temperature, to over five mole percent at greater depths. The observed variations of composition with depth were contrary to what would be expected from gravity-chemical equilibrium considerations. We propose that the dominant process for compositional grading in the Khuff is the generation of hydrogen sulfide by thermo-chemical reduction of sulfate. This process is believed to occur at temperatures above a threshold value (about 270 0F for the Ghawar Khuff), and utilizes hydrocarbons as one group of reactants. Thus, as is shown in the paper, hydrogen sulfide composition increases with depth at the expense of hydrocarbons in a way that upsets the effect of gravity- chemical equilibrium. P. 685
- Asia > Middle East > Saudi Arabia > Eastern Province > Al-Ahsa Governorate > Arabian Basin > Widyan Basin > Ghawar Field > Lower Fadhili Formation (0.99)
- Asia > Middle East > Saudi Arabia > Eastern Province > Al-Ahsa Governorate > Arabian Basin > Widyan Basin > Ghawar Field > Khuff D Formation (0.99)
- Asia > Middle East > Saudi Arabia > Eastern Province > Al-Ahsa Governorate > Arabian Basin > Widyan Basin > Ghawar Field > Khuff C Formation (0.99)
- (7 more...)
- Reservoir Description and Dynamics > Formation Evaluation & Management > Drillstem/well testing (1.00)
- Reservoir Description and Dynamics > Fluid Characterization > Phase behavior and PVT measurements (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
- Health, Safety, Environment & Sustainability > Health > Noise, chemicals, and other workplace hazards (1.00)