CHRONOSTRATIGRAPHICALLY BASED RESERVOIR MODEL FOR CENOMANIAN CARBONATES, SOUTHEASTERN IRAQ OILFIELDS

The Cenomanian – Turronian sedimentary succession in the south Iraq oil fields, including Ahmadi, Rumaila, Mishrif and Khasib formations have undergone into high-resolution reservoir-scale genetic sequence stratigraphic analysis. Some oil-wells from Majnoon and West-Qurna oil fields were selected as a representative case for the regional sequence stratigraphic analysis. The south Iraqi Albian – Cenomanian – Turronian succession of 2nd-order depositional super-sequence has been analyzed based on the Arabian Plate chronosequence stratigraphic context, properly distinguished by three main chrono-markers (The maximum flooding surface, MFS-K100 of the upper shale member of Nahr Umr Formation, MFS-K140 of the upper Mishrif carbonates, and MFS-K150 of the lower Khasib shale member).Three 3rd-order genetic mega-sequences were embraced between the cited chrono-markers. The markers have been considered as regional key-surfaces for the Late Albian – Cenomanian to Early Turonian and Late Turonian to Early Coniacian stratigraphy of the south Iraqi oil fields. Eight 4th-order genetic meso-sequences (MS1 to MS8) have been established, comprising multiple 5th-order high-frequency (HF) lithofacies cycles, successively arranged in the mega-sequences without disturbance. MFS-K135 (this study), MFS-K140, MFS-K150 and Seven successive regional chrono-markers [MFS-K120, MFS-K125 (this study), MFS-K130, and MFS-K160 of upper Khasib shale member] started from lower Ahmadi shale member, identify these meso-sequences. Associated fifteen key-surfaces (K121, K122, K123, K124, K125, K126, K127, K128, K129, K131, K132, K133, K134, K141 & K142) have been described as well. The meso-sequence 1 signifies Ahmadi lithofacies buildups, whereas; the other meso-sequences represent Mishrif lithofacies buildups. The Rumaila carbonates come across the first HST-unit of the meso-sequence 2. The meso-sequence 8 represents the Khasib carbonate facies buildups. The depositional super-sequence is terminated by type-1 sequence boundary SB-K150 at the top of the Mishrif Formation, created by maximum regression (MR). The study declares 15 reservoir syn-layers and 9 non-reservoir layers; each is essentially characterized by HF-single-lithofacies-cycle and lateral continuity pattern. This syn-layer model can be used as sequence steering technique for carbonates heterogeneity aspects, in the south Iraqi oil fields to control fluid dynamics in primary and secondary development projects

A MODIFIED WATER INJECTION TECHNIQUE TO IMPROVE OIL RECOVERY: MISHRIF CARBONATE RESERVOIRS IN SOUTHERN IRAQ OIL FIELDS, CASE STUDY

A modified water injection technique has organized by this study to improve oil recovery of the Mishrif reservoirs using polymerized alkaline surfactant water (PAS-Water) injection. It is planned to modify the existing water injection technology, first to control and balance the hazardous troublemaker reservoir facies of fifty-micron pore sizes with over 500 millidarcies permeability, along with the non-troublemaker types of less than twenty micron pore sizes with 45 to 100 millidarcies permeability. Second to control Mishrif reservoirs rock-wettability. Special core analysis under reservoir conditions of 2250 psi and 90 °C has carried out on tens of standard core plugs with heterogeneous buildup, using the proposed renewal water flooding mechanism. The technique assures early PAS-water injection to delay the water-breakthrough from 0.045 – 0.151 pore volumes water injected with 8 – 25% oil recovery, into 0.15 – 0.268 pore volumes water injected with 18 to 32% improved oil recovery. As well as, crude oil-in-water divertor injection after breakthrough, within 0.3 to oil0.65 – 0.85-pore volume of water injected to decrease water cut 1 four 0 to 15%. The overall progress of the PAS-water injection has achieved residual oil mobility of 65%, and upgraded the 35 – 50% oil recovery range by less than three pore volume water injected with 20 – 60% water cut, compared with the same oil recovery range by more than ten pore volume water injected with around 70% water cut. The ultimate oil recovery improved by this technique is from 70% via more than 20 pore volume water injected with over 95% water cut by usual water injection, to 85 – 90% via 6.4 pore volume water injected with over 90% water cut by the modified water injection. The technique succeeded to lower the end-point mobility ratio to 1.5 from above five by usual water injection. It is highly recommended to use ten micron mesh filter at the main injection site and four or five micron mesh filter at the injector sites; to avoid more than 80% of the suspended particles and save as much as possible the overall reservoir facies from permeability damage

The Origin and MgCl2–NaCl Variations in an Athalassic Sag Pond: Insights from Chemical and Isotopic Data

The examination of past and new chemical–isotopic data (2H/1H–18O/16O,11B/10B and87Sr/86Sr ratios) shows the meteoric origin of the Sawa Lake (Muthanna Governorate, Iraq) and its connection with the local aquifers, which feed the lake via the groundwater emerging from its floor through fault systems. The chemical and isotopic evaporation models are traced by geochemical computer codes by using a different composition of some potential inflows to the lake (e.g., the Euphrates River and Dammam aquifer). The main product of the chemical evaporation models is gypsum, as confirmed by the mineralogical examination of the sediment and the surrounding outcrops. A strong18O–2H enrichment is a consequence of the evaporation effect in arid regions; δ18O–Cl models and δ11B = + 23.4‰ exclude the contribution of any seawater-derived fluids. This latter value along with87Sr/86Sr = 0.707989 suggests a mixed origin from the Eocene–Miocene aquifers. The isotope and chemical evaporation paths from the meteorically recharged sources match the lake composition. However, compositional switches from NaCl toward MgCl2occurred in the last decade and are related to post-drought periods, showing that the interaction of the recharging waters with the local soils (Na–Mg exchange and/or the leaching of the top layer salts) have a role in the chemical composition. This demonstrates that the lake is significantly influenced by climatic variations