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Abstract Exploration offshore Mediterranean in Egypt is getting more and more important due to gas reserve discovered by IEOC in Port Fouad, Baltim and Temsah concessions. This paper will discuss some of the challenges required to drill safely and economically through the overpressurized sensitive shales of Nile Delta basin. It also summarises the problems encountered while drilling the very high pressure wells in Port Fouad and Temsah concessions, such as: hole instability, mud problems, water and gas kick, overpressure detection, lost of circulation, casing setting depth and related design, running and cementing operations, environmental pollution, safety and logistic problems. Experience gained from the past and undergoing drilling operations in offshore Mediterranean is included in this paper and it could be a support for future exploration and development in the area. Introduction IEOC started it's exploratory operations in the Nile Delta and offshore Mediterranean across the Nile Delta in the early sixties. Since then a considerable exploration work extended for more than 30 years and covered most of the Nile Delta, East Delta, North Sinai and offshore Mediterranean, this activity had proved huge amounts of gas reserve in land and offshore concessions (Abu Madi, Qantara, El-Qara, East Delta, Port Fouad, Wakar, Baltim and Temsah). Recently great attention has been paid to explore and develop the existing fields in offshore Mediterranean, (figure-1), due to the strategic gas reserve proved in the area. Because considerable operating difficulties were encountered while drilling the exploratory wells, an ambitious attention is being paid by IEOC to determine, evaluate and find the optimum solution for these difficulties. These difficulties and the nature of the wells cause particular challenges for drilling engineers and rig personnel. These include: A-Considerable depth at which the reservoirs are encountered 3600-4700 m. required relatively long drilling sections and heavy casing strings. B-High reservoir pressure, where 10,000 psi. drilling equipment is being operated and tested at the limit of its working pressure design. C-Complex overpressure regime of the Nile Delta basin which require sophisticated and heavy casings with the need to set 20" casing over 1000 m. as surface casing. D-High overpressure zones are encountered from the middle of Kafr El-Sheikh formation down to Qantara and Tineh formations requiring high mud weights up to 1.85 to 2.2 s.g. and more to control formation pressures between 9000 and 12000 psi. E-Limited margin through the pore pressure gradient and the fracture gradient, specially in high pressure directional wells, resulting very limited choke margin and kick tolerance. This needs a continuous and accurate prediction, detection and evaluation of the formation pore pressure and fracture gradient, before, while and after drilling. Consequently, it requires an extensive engineering work and an accurate data evaluation. F-Hole instability problems while crossing the highly sensitive overpressurized shales of Kafr El-Sheikh and the subsequent formations with the need to a complex drilling fluid that was recently optimized with oil base mud (OBM). G-High potential gas and water flow while and after cementing jobs and the need to optimize cement design and cementing operations. P. 281
Abstract Exploration drilling in the Nile Delta has dramatically risen over the past 3 years, jumping from 5-10 wells/year up to 20-25 wells/year. Much of this recent drilling has been targeting the highly successful Pliocene play trend and the 2008 industry success ratio approached a phenomenal 90%. Thick sequences of Pliocene deep marine sediments have been successfully drilled and led to several offshore gas discoveries. No great exploration interest had been directed towards these good reservoirs in the onshore areas of the Nile Delta. Nevertheless, Dana Gas has been one of the most active and successful operators for this exploration target in its West El Manzala and West El Qantara Concessions. The gas sands of the Pliocene reservoirs are characterized by low velocities and densities compared with the surrounding shales and, subsequently, the top and base of the reservoirs have a "bright?? seismic amplitude response. Additionally, the gas charged Pliocene reservoirs are often associated to acoustic impedance anomalies presence. The key challenge in the Pliocene reservoirs exploration is to understand the depositional environment with respect to the amplitude and acoustic impedance geometry from 3D seismic data through the cross-correlation between seismic facies character and the depositional pattern and environment. The main features and variations recognized in the reservoirs drilled to date in West El Manzala and West El Qantara Concessions show a slow activity in the main basin evolution stage that seems to be not affected by high turbidity current flow or significant slope channeling. The early stage broad and straight channel system valley was cut and filled by younger channelized systems. Minor incisions of channel cuts are considered to be a key feature in defining channel fill development and sand distribution.
Abstract Oil-based fluids (invert emulsion fluids) have for many years been the fluid of choice for use in challenging hole sections. These fluid systems can bring many advantages, including optimal shale stability, low torque and drag, good resistance to contamination, and high drilling rates. One of the challenges of utilizing an invert emulsion fluid, however, has been the increasing level of environmental concern and legislation associated with its use. These challenges have driven the search for a high performance water-based fluid that will provide oil-based fluid performance and be environmentally acceptable in all offshore areas of the Egyptian Mediterranean Sea. A novel, environmentally compliant high performance water-based fluid (HPWBF) system has been developed that has proven to be extremely inhibitive and highly lubricious. Use of this new HPWBF system has helped operators to drill some of the most reactive shales in the Egyptian Mediterranean Sea while avoiding the high cost and safety risks associated with "skip and ship" operations. This performance is coupled with excellent cuttings integrity, increased temperature stability and good hole-cleaning properties. In the application of this system, the engineered approach matches fluid requirements with local clay characteristics, environmental regulations and operational objectives. A HPWBF was chosen to drill Petrobel's well Karam-1 with a great success. The fluid was utilized to drill 334 meters of 12¼" hole section through the very challenging highly reactive formation of Kafr El-Sheikh stratum. The following conditions existed for this operation: Fluid must be water-based to meet environmental stipulations The shale section would be exposed for up to 10 days while logging Bottomhole temperature is 230°F Approximately 100 m 17½" rat hole existed below the 13 3/8" casing This paper discusses the technical challenges and highlights the criteria for the proposed fluid system and the successes achieved in this well.
Hole instability in Nile Delta area, specially in the Middle and East leases is one of the main drilling problems encountered in most of the wells drilled either by Petrobel or Nidoco. Shale swelling, caving, tight holes, and consequently loss of circulation problems were experienced and overcame using several techniques. This paper is focused on the analysis of the main drilling hazards related to shale instability including analysis of pore pressure data obtained from sonic, sigma, and RFT logs and prediction of pore pressure expected in the forecasted wells. It discusses the different mechanisms of Mile Delta shale instability. Field observations and results of X-Ray diffraction analysis of shale samples collected from the area wells led to a significant improvement in shale stability by using potassium polymer mud instead of sodium chloride lignosulphonate mud. Also tight hole and differential pipe sticking possibilities while drilling through low pressure porous sands were reduced by using ultra fine cellulosic materials.
Conclusion and recommendations for drilling performance optimization are included in this paper.
Abu Madi gas field located in the northern part of Nile Delta, discovered by IEOC in 1967 and completed and developed by Petrobel, fig.(1).
Maintaining a stable borehole is one of the main objectives while drilling gas wells in Nile Delta area. Hole instability in the area takes several forms, soft ductile bentonitic shale squeezed into the hole, hard brittle geopressurized shales that spall under stresses, and caving due to swelling pressure, with consequent hole enlargement and bridging. This results-in disasters such as stuck pipe and sidetracked hole.
Also, loss of circulation into high porosity unconsolidated Sands of Mit Ghamr and through depleted sands of Abu Madi formations, with its consequent related drilling and mud problems, was encountered. These problems adversely influence drilling efficiency and cost. Analysis of 33 wells drilled in the area showed significant variation according to mud type, formation pressure and drilling practices.
The followings are the main challenges to drill a trouble free well in Nile Delta: 1- Optimum mud weight to drill through Kafr El Sheikh shales based on its actual pore pressure. 2- Optimum mud type to alleviate the hole instability problems experienced while drilling Kafr El Sheikh, and the lower formations. 3- Optimum casing design for exploratory and development wells. 4- Optimum Nile Delta drilling practices.
One of the practical and reliable procedures for detecting and investigating hole instability problems is, to determine the actual formation pore pressure anomalies within Kafr El Sheikh and. Sidi Salem shales, to identify the clay minerals present in the problematic shale, to select the optimum mud system and to evaluate the area drilling practices.
I - ORIGIN OF OVER PRESSURE according to Fertle and others, origin of overpressure can be due to several factors. In Nile Delta area, the over pressure encountered through Sidi Salem and Kafr El Sheikh is mainly due to overburden and tectonic effects.
SIDI SALEM FORMATION
Overburden effect; Sidi Salem formation deposited after the pronounced flexure affected Pre-Miocene formations extending E-W across the mid-Delta area resulted Delta basin shown in figure 3 during the Middle Miocene age in deep marine environment (outer shelf). The formation is composed of thick body ( 700m) of shale containing few sand levels near its top. As the main composition is shale, the fluid remained trapped in the shale and as the zone exposed to the subsequent over burden loads (+3400 m) the pore pressure built up above the hydrostatic value. Tectonic effect; The high rate of subsidence of the basin while sedimentation of the overlaying deltaic sediments of Qwasem formation created differential compaction gravitational faults, in addition to some tectonic movements during late Messenian which created some tectonic stresses, faulting and diaper of Sidi Salem shale through Qwasem and Abu Madi formation.
In the last decade, the Plio-Pleistocene succession is considered as the major gas prone play in Nile Delta province due to the favorable convergence between technical and economical conditions. The present study addresses the Plio-Pleistocene depositional elements as a key for unrevealed potential in the Eastern Mediterranean basin. Discoveries mainly driven by the detection of direct hydrocarbon indicators (DHIs) are concentrated in the eastern growth fault domain that developed along the distal Nile Delta slope. Moreover, the reservoir characteristics and the trapping mechanism are strictly related to the presence of syn-sedimentary growth listric faults. The target reservoirs are mainly composed of sandstone of turbiditic origin, which corresponding to bright seismic amplitude anomalies. The lithofacies of the investigated interval is dominated by thin bedded fine-grained sediments (i.e. heterolithics facies).
The interpretation and analysis of seismic attributes and amplitude anomaly maps of this interval showing NW-SE anomaly trends that reflecting the impact of syn-sedimentary growth listric faults (salt tectonics) on the reservoir facies distribution in this area. Furthermore, such seismic attribute analysis and interpretation are used to identify different depositional architectural elements of the reservoir facies that are (1) massive thick bedded sandstone facies (stacked lobes), (2) channel fill deposits facies, and (3) heterolithic levee facies. These could be confirmed from the facies analysis using core description and wireline logs along with borehole image data analysis.
The reconstruction of the depositional architectural elements of the studied succession and its stratigraphic pattern contributed to put in a context the recent discoveries and to outline the residual potential of the post-Messinian section in this area. Beside to the traditional DHI supported sand prone targets, this sector is characterized by unconventional silty and fine-grained reservoirs, referable to turbidite channel-levee complexes. Although, this facies is usually overlooked in conventional reservoir evaluation, a good production performance in recently drilled wells has been recorded.