Zubair Oilfield Research Articles

Geomechanical Analysis to Avoid Serious Drilling Hazards in Zubair Oilfield, Southern Iraq

Zubair oilfield is an efficient contributor to the total Iraqi produced hydrocarbon. Drilling vertical wells as well as deviated and horizontal wells have been experiencing intractable challenges. Investigation of well data showed that the wellbore instability issues were the major challenges to drill in Zubair oilfield. These experienced borehole instability problems are attributed to the increase in the nonproductive time (NPT). This study can assist in managing an investment-drilling plan with less nonproductive time and more efficient well designing.
 To achieve the study objectives, a one dimension geomechanical model (1D MEM) was constructed based on open hole log measurements, including Gamma-ray (GR), Caliper (CALI), Density (RHOZ), sonic compression (DTCO) and shear (DTSM) wave velocities , and Micro imager log (FMI). The determined 1D MEM components, i.e., pore pressure, rock mechanical properties, in-situ principal stress magnitudes and orientations, were calibrated using the data acquired from repeated formation test (RFT), hydraulic fracturing test (Mini-frac), and laboratory rock core mechanical test (triaxial test). Then, a validation model coupled with three failure criteria, i.e., Mohr-Coulomb, Mogi-Coulomb, and Modified lade, was conducted using the Caliper and Micro-imager logs. Finally, sensitivity and forecasting stability analyses were implemented to predict the most stable wellbore trajectory concerning the safe mud window for the planned wells.
 The implemented wellbore instability analysis utilizing Mogi-Coulomb criterion demonstrated that the azimuth of 140o paralleling to the minimum horizontal stress is preferable to orient deviated and horizontal wells. The vertical and slightly deviated boreholes (1ess than 30o) are the most stable wellbores, and they are recommended to be drilled with 11.6 -12 ppg mud weight. The highly deviated and horizontal wells are recommended to be drilled with a mud weight of 12-12.6 ppg.

ELEMENTS DISTRIBUTION FOR THE UPPER SANDSTONE MEMBER OF THE ZUBAIR FORMATION IN ZUBAIR OIL FIELD, SOUTHERN IRAQ

The upper sandstone member (Z/2) is one of the most important reservoirs in the Zubair Oilfield, south of Iraq. It belongs to the upper part of the Zubair Formation, the Lower Cretaceous age, and deposited in deltaic environments. The upper sandstone member consists of several sandstone units which are isolated by the shale units. Major trace and rare earth elements (REEs) of the upper sandstone member in Zubair Formation have been analyzed. Six core samples were used to determine the source of sediments, paleo-environment redox condition and elements concentrations. The geochemical analysis data indicate that the source of sediments rock was influenced by a low to moderate degree of weathering conditions in the Hammar and Safwan Domes. The results have shown that all samples were formed in an oxic environment, with humid paleoclimate. Geochemical analysis data indicate that all rock samples are fundamentally derived from rhyolitic and andesitic rocks more a felsic source. The results show that the samples are mainly of marine organic matters input. The values of Chemical Index of Alteration in the Hammar Dome range from 13.05 to 24.37, while from 23.72 to 77.22 in the Safwan Dome. These results may attribute to fine and medium clastic sedimentary rocks in the H sandstone unit, with a low degree of weathering in the Hammar Dome, and high to medium with slightly higher abundance of clayey silts in the Safwan dome.

PVT and Pressure Analysis in Third pay Reservoir of Zubair Oilfield Southern Iraq

In this paper the pressure drop and PVT data that used in the model to describe the behavior ofreservoir fluids of 3rd pay reservoir of Zubair field is explained. The wells in Hammar-Shuaiba area showhigh Gas Oil Ratio, exceeding 1,000 scf/stb. This is bad sign and that mean reservoir pressure is reducedramatically and gas will produced , finally the energy that use to push the oil from reservoir to thesurface will decrease. Eleven samples have been collected and analyzed from all 3rd pay reservoirs overthe years, seven samples in Hammar –Shuaiba area. The PVT data resulted to be scattered, being notpossible to define any acceptable conclusion about their trend versus depths, taking also into account thatthey are not referred to the same temperature. The main difference between the old and new PVT is theBubble Point pressure at reservoir conditions, which increases from 2646 psi to 2760 psi. Historicalpressure behavior shows that water Injection is beneficial to maintain stable pressure trend. Pressureanalysis shows a strong depletion start from 2013 in various zones of Hammar Shuaiba domes.

Building 1D Mechanical Earth Model for Zubair Oilfield in Iraq

Many problems were encountered during the drilling operations in Zubair oilfield. Stuckpipe, wellbore instability, breakouts and washouts, which increased the critical limits problems, were observed in many wells in this field, therefore an extra non-productive time added to the total drilling time, which will lead to an extra cost spent. A 1D Mechanical Earth Model (1D MEM) was built to suggest many solutions to such types of problems. An overpressured zone is noticed and an alternative mud weigh window is predicted depending on the results of the 1D MEM. Results of this study are diagnosed and wellbore instability problems are predicted in an efficient way using the 1D MEM. Suitable alternative solutions are presented ahead to the drilling process commences in the future operations.

3D mechanical earth model for Zubair oilfield in southern Iraq

During drilling operations, wellbore instability is one of the reasons that increase nonproductive time (NPT). Maintaining a stable wellbore is the primary importance during drilling by applying a proper geomechanical model to analyze and understand the distribution of stresses around the wellbore in order to minimize drilling risk and NPT. The lack of any geomechanical studies in Zubair oilfield in southern Iraq is one of the reasons that lead to wellbore stability-related problems and thus an increase in NPT. Petrel Geomechanics 2018 was used to show the distribution of the stresses and the mechanical properties. Showing the distribution of stresses in 3D MEM has big advantages in several ways, and one of them is to select the best path for any future directional wells. To mitigate wellbore stability problems and depending on the 1D mechanical earth models (MEM) results, a detailed 3D MEM was built for Zubair oilfield as the method to precisely pinpoint and diagnose those problems. The results of this study show two points; first is an abnormally pressured zone in Tanuma shale formation, and second, a narrow mud weight window in front of the Tanuma formation. As a conclusion, the mechanical earth model was an efficient tool in diagnosing and predicting geomechanics-related problems, thus suggesting an alternative mud weight program for the problematic zone, which is more important to reduce the most essential factor in the NPT.

Wellbore Breakouts Prediction from Different Rock Failure Criteria

One of the wellbore instability problems in vertical wells are breakouts in Zubair oilfield. Breakouts, if exceeds its critical limits will produce problems such as loss circulation which will add to the non-productive time (NPT) thus increasing loss in costs and in total revenues. In this paper, three of the available rock failure criteria (Mohr-Coulomb, Mogi-Coulomb and Modified-Lade) are used to study and predict the occurrence of the breakouts. It is found that there is an increase over the allowable breakout limit in breakout width in Tanuma shaly formation and it was predicted using Mohr-Coulomb criterion. An increase in the pore pressure was predicted in Tanuma shaly formation, thus; a new mud weight and casing programs are proposed to overcome such problems in the drilling operations in field developments plans.

Present-day in situ Pore Pressure Distribution in the Tertiary and Cretaceous Sediments of Zubair Oil Field, Iraq

Present-day in situ Pore Pressure Distribution in the Tertiary and Cretaceous Sediments of Zubair Oil Field, Iraq

Structural geology and petrophysics analysis to Injection wells of Mishrif Formation in Shuaiba Dome – Zubair Oil Field

Mishrif formation is the one of the most important reservoir in Southern – Iraq and the injection water important to support the reservoir pressure. The current study combined the interpretations of PLT, structural geology and petro-physics to understand the distribution of the injection rate for nine injection wells to the Mishrif Formation in Shuaiba Dome (or culmination) - Zubair Oil Field. PLT analysis calculated injection rate for Mishrif Formation, structural analysis included geometric and genetic analysis, whereas petrophysics analysis used open hole logs interpretation and core data for the injection wells to determine the petro-physics characteristics (especially the distribution of porosity and permeability). The current study concluded that the injection rate, porosity and permeability of Mishrif Formation distributed unequally across it. This variation is almost regular, whereas the Upper Mishrif more than Lower Mishrif, while Middle Mishrif get the least value. The thickness of Lower Mishrif more than Upper Mishrif. This may affected by a folding mechanism due to tectonic activity (reactivated basement faults and Hormuz salt structures).

Converting Zubair oil field permanent power generation from single cycle into combined-cycle with plant exergy analysis

The combined-cycle power plant is the effective way to increase power and thermal efficiency which can rise thermal efficiency up to 50% corresponding to low heat value of the fuel (LHV). This study focused on converting Zubair Oil Field Gas turbine (ALSTOM GT13E2) from single cycle into a combined cycle power plant. Models suggestion design have been presented with back-pressure steam turbine by Cycle-Tempo (5.1) thermodynamics simulation program, which presents value diagram and exergy flow diagram both are useful to understanding the thermodynamic performance of complicated systems.The result of exergy analysis explicate that huge amount of exergy loss firstly occurs in gas turbine combustor (about 60% due to high irreversibility), and heat recovery steam generation (HRSG) is the second major exergy loss in combined cycle power plant (about 30%) recently apparatus concepts less than 10% of exergy (like compressors and expanders). Also, in this study explained the effect of changing the ambient temperature on the performance of power plant by using four temperature parameters on the four simulation models at constant compression ratio. The results were the increase in gas turbine temperature inlet led to decrease the net power output of the CCPPs. Thermal and exergy efficiencies increase when ambient temperature increase due to growth turbine inlet temperature but this temperature restricted by creep rupture and thermal fatigue for combustor parts and turbine blades metal. Maximum thermal and exergy efficiencies can be reached to 55.74, 53.28% respectively at worst ambient temperature. The calculation results in this study were compared with two previous studies, with considerable differences in input parameters of the gas turbine and steam turbine also, the types of the gas turbine models. finally, the results showed acceptable agreement.

WELL LOGGING AND ELECTROFACIES OF ZUBAIR FORMATION FOR UPPER SANDSTONE MEMBER IN ZUBAIR OIL FIELD, SOUTHERN IRAQ

The Lower Cretaceous Zubair reservoir is a main producing horizon in the Zubair oil Field, southern Iraq. The reservoir consists of a number of isolated vertical major sandstone units. Sedimentary characteristics can be determined using the well log data as one of the most fundamental methods for reservoir characterization in the oil and gas industry. The reading of high gamma-ray response indicates the presence of shale which contains clay minerals, K-feldspar, and organic material that emits natural gamma radiation. The clean sandstones emit less radiation so it has a lower gamma-ray count analysis. Five of electrofacies were identified in the upper sandstone member of Zubair formation in Zubair oil field, in more details H layer divided into three sub-units. Zubair formation delta deposited through sea regression followed by sea progression because shelf facies overlies other delta facies as shown H layer between K and C units both were shale rocks. Porosity and permeability of the upper sandstone member of Zubair Formation were identified in twenty oil-wells. The relationship between the porosity and permeability after correction with data obtained from the core analysis data showed an improvement to the north part of the field precisely in Hammar-Shuaiba domes. On the other hand the grain sizes varied from coarse to medium; medium to fine in Hammar dome while fine to medium fine to very fine with clay influence led to a decrease the porosity and permeability thus reduced oil production.

Torque and Drag forces challenges in highly deviated oil well (Zubair oil field)

The benefits from doing this analytical study in order to be able to measure and predict the frictional forces affecting a drill string and wellbore (Torque and drag) by construct model of well plan software, hence; the high deviated and directional wells must be planned to keep the torque and drag forces at a minimum and allowable limit.
 Also, knowledge of the drill string phenomena can give us an opportunity to choose drill string components that consider these extra forces involved in the operations "high torque and drag values" in directional sections.
 In addition to knowledge of influence torque and drag on planned well trajectory can give us a good idea and lesson learned to consider this challenges in the next planned well profile. As a result of well path design one of the best ways to reduce torque and drag forces.
 One deviated well in Zubair oil field named, ZB-348 have been selected for analyses torque and drag problems and study the effect of (friction factor, well profile and drill string design) on the mentioned problem.
 Well data include hole section size, fluid properties, well profile survey, rig specification, drill string details and drilling parameters were used in well plan software from landmark worldwide programming group to make a comparison between actual and planning status.
 The results show a difference between planning and actual case when drilling 12.25" hole and found the root causes for this difference are high flow rate, tortuosity, well bore instability and complete losses. 
 The maximum torque about (20 klb-ft) and drag value approximately (30 klb).

Determination of Horizontal Stress Orientations from Borehole Breakouts in Zubair Oilfield, Southern Iraq

Determination of Horizontal Stress Orientations from Borehole Breakouts in Zubair Oilfield, Southern Iraq

Assessment of Some Heavy Metal Concentrations in Drilling Mud samples in Az Zubair Oil Field, Basra, Iraq

Assessment of Some Heavy Metal Concentrations in Drilling Mud samples in Az Zubair Oil Field, Basra, Iraq

Chemical, physical characterization and salinity distribution of the oilfield water in the Upper Sandstone Member of the Zubair reservoir at Rumaila North Oilfield, Southern Iraq

The oilfield water in the Upper Sandstone Member of the Zubair reservoir (Barriemian-Hauterivian) at Rumaila North Oil Field was investigated for the interpretation of salinity and geochemical evolution of brine compositions. The interaction of the oilfield water with reservoir rock resulted in a brine water derived from the marine water origin of partial mixing with meteoric water similar to the compositional ranges of formation water from Gulf of Mexico offshore/onshore Mesozoic reservoirs. The high TDS (207350- 230100; average 215625 mg/L) is consistent with the electrical conductivity (340362-372762; average 351024μs), and predominantly represented by Cl (123679 mg/L) as anions and (29200 and 14674 mg/L) for Na and Ca as cations respectively. The contribution of cation (epm%) are as Na (70.2), Ca (18.9), Mg (8.1) and K (1.7); and anion as Cl (99.7), SO4 (0.25), HCO3 (0.07) and CO3 (0.005). sodium (57550-60500mg/L) is greater than of seawater six times, calcium and magnesium three times greater, and chloride 6.5 times greater, but Sulfate is depleted to six times less due to a sulfur release from sulphates and link with different hydrocarbon species, precipices as native sulphur and link with hydrogen forming H2S. The Zubair oilfield water is characterised by acidic pH (pH=5.2- 5.77) enhanced petrophysical properties, high specific gravity (1.228) predicts a high fluid pressure (4866 psi), hydrocarbon saturation (0.43%), water saturation (0.57%) and porosity (12.7). The Mineral saturation model indicates that the Zubair oilfield water is an unsaturated water with respect to all suggested minerals at 5.45, but at simulated pH, brucite being an equilibrium at pH 9.12, but brucite and portlandite being supersaturated at pH 11.9. The mineral solubility responses to the changes in temperature, pressure, pH, Eh, and ionic strength, thereby formation damage is proportionally developed.

Assessment of naturally occurring radioactive material (NORM) in the oil drilling mud of Az Zubair oil field, Basra, Iraq

The concentration of naturally occurring radioactive material (NORM) in oil drilling mud samples collected from 14 geological formations begins with Dibdibba Formation depth (140–150 m) and ends with Ahmadi Formation depth (2764.5 m) of the oil well in Az Zubair oil field (ZB-296) in Basra governorate were determined using NaI gamma spectrometer. Gamma spectrometric analyses of natural radionuclides 238U, 232Th and 40K have indicated average concentrations in Bq kg−1 as 614.5, 233.0 and 6201.4 Bq m−3, respectively. Radon levels and radium contents for different formations were measured using solid state nuclear track detector CR-39. The obtained values of radon concentration were ranged from 209.3 to 1876.6 Bq m−3 and the values of radium content ranged from 0.76 to 6.79 Bq kg−1 for Tayarat and Sa’adi formations, respectively.

IDENTIFICATION OF PALYNOZONES AND AGE EVALUATION OF ZUBAIR FORMATION, SOUTHERN IRAQ

Fourteen rock selected samples from lower and middle parts of Zubair Formation in Zubair 109 (Zb-109) and Zubair 43 (Zb-43) boreholes of Zubair oil field at southern Iraq, they have been subjected to standard palynological processing techniques were used to extract the acid resistant organic matter. Microscopic analysis of the sedimentary organic matter of the two boreholes revealed abundant and diverse palynomorphs of (35) species of spores belonging to (23) genera, (9) species of pollen grains belonging to (6) genera and (21) species of dinoflagellate cysts belonging to (13) genera. Two assemblage palynozones have been also identified based on the index palynomorphs contained in each zone. The age assignment of each palynozone is based on international correlation with Australia, Middle East and Europe countries.