Well bore cleanouts have been performed for many years with coiled tubing and it may be said that the cleanout operation is one of the most routine services performed in the coiled tubing industry; but until recently design was no more than a rule-of-thumb approach. Sufficient information is now available to facilitate informed decisions and achieve reliable engineering solutions, utilizing a sophisticated particle transport model. A methodical thought process, based on extensive research and mathematical modeling, will be presented for designing specific well bore cleanouts in a challenging offshore field in the Middle East. Case histories from a number of wells are documented detailing the conclusions from each. Laboratory analysis was performed on samples collected from the cleanout operations to further optimize and validate the design process. It is the intent of this paper to demonstrate the importance of sound engineering design, aided by comprehensive computer modeling technology. Introduction Particle transport is a process to remove material such as formation fines, drill cuttings, sand, etc. out of wells. The use of coiled tubing to convey circulation fluids and tools to facilitate a thru-tubing cleanout is considered standard industry practice in the oilfield. Typical fluids used to facilitate these operations are water, brine, and water based gellant systems. Hydrocarbon fluids may also be pumped, however inherent HSE issues must be addressed when pumping hydrocarbon fluids. It may be safe to say that "cleanouts with coiled tubing is the number one application". Having said that, one may also say that the industry has really lacked a good understanding of how to effectively transport particles. The fact that regular operations are conducted on a daily basis globally does not necessarily mean that everyone conducting cleanout operations has a full understanding of how to effectively design and execute a particular cleanout. Based on a comprehensive experimental test of solids transport in the previous studies1–7, a patented fill cleanout process technology8 with CT has been developed and proved by field operations9–13. The process includes running CT into the well while circulating fluid using a nozzle with a "high energy" jetting action pointing forwards down the well to stir up the particulate solids and allow the CT to reach a target depth or bottom of the well (penetration stage). When the bottom or desired depth is reached, the hole can then be cleaned either by circulating a fluid while keeping the CT stationary (circulation stage) or by pulling the CT out of the wellbore with continuous circulation (wiper trip stage), or by a combination of these stages. In the wiper trip mode, a reversing jetting nozzle with low energy is used to circulate the fluids and to create a particle re-entrainment action to enhance agitation of the solids and then entrain the particulates in suspension for transport out of the wellbore while pulling the CT out of the hole. The reverse jetting action along with a controlled pump rate and POOH speed can produce a solids transport action which cleans the hole completely by keeping the solids in front (upward) of the end of the CT in continuous agitation. The low energy nozzles have a low pressure drop which allows for higher flow rates and results in improved cleanout efficiency. This method and tool is more efficient than existing methods since the process may be limited to one pass or sweep with the option of resetting the tool for repeated cycles if required. Factors Affecting Clean Out Operations There are several factors which affect the clean out operation and hence the efficiency of the clean out job. When designing a clean out job, those factors should be taken into consideration to achieve a successful clean out job Fill type: Fill type plays an important role in sand clean out design. Fill type can be fines (small grain size) or coarse (large grain size). The fill type affects fluid selection, penetration and wiper rate determination. The larger grain size is more challenging to transport in a cleanout job. The density is related to the circulation time (how long to circulate at TD to move heavy solids out of well). The fundamental reason for circulation and turbulent flow is to prevent solids falling back into the well when performing a wiper trip.
Fiber optic enabled coiled tubing (FOECT) has been commonly used in qualitatively evaluating reservoir matrix chemical treatment in real time during the past couple of years. During this period, attempts of transforming qualitative evaluations to quantitative ones were made. The quantitative evaluation is based on two simultaneous criterions. The first one is a downhole pressure diagnostic plot (pressure transient analysis) created instantinuously using real-time acquired data by the downhole gauges. The second is an estimate of the zonal coverage based on the resulting temperature profile plot before, during and after a pumping treatment. Pressure transient analysis gives the skin as a direct output, while the cooling down/warming up DTS profiles identifies where the treatment fluids went in the formation, hence identifying the damaged zones. It is strongly recommended to combine well testing analysis techniques with zone coverage evaluation in highly deviated and horizontal completed wells in both clastic and non-clastic rocks. Basically, deriving the skin from the injectivity test (pretreatment) and the skin from the post flush (post-treatment) provides an evaluation matrix treatment effectiveness. A comparison between formation damage "skin" before and after the treatment was performed on the spot, revealing positive results of nearly uniform distribution of treatment fluids, and skin value reduction across the 3400 ft horizontal section. Following the innovative procedures executed in well-A, different techniques were proposed, providing time and cost savings; raising the operational excellence expectations levels higher than expected for an offshore environment. The application of FOECT technology helped to minimize uncertainties during treatmentevaluation, and enhanced treatment distribution and placement. In addition to establishing more accurate and reliable Nodal Analysis and production forecast models.
Effective mudcake removal is essential to restore the optimal well productivity/injectivity after different drilling operations. Typically, this objective is achieved by using harsh chemical treatments such as hydrochloric acid (HCl), organic acids and oxidizers. However, these methods have been limited due to associated high corrosion rates, high operation cost, and un-even mudcake removal. This task becomes even more difficult and very challenging in horizontal/multilateral wells. Organic acids and acid precursors have been also used to clean long horizontal wells following drilling operations. However, in long multilateral horizontal wells, fluid placement is considered one of the main challenges with chemical mudcake removal treatments due to accessibility to each lateral and reaching its TD. Additionally, the use of these treatments has poor health, safety and environmental (HSE) footprints. This work provides a workflow and illustrates the use of an in-house designed zero-flaring flowback system to clean up recently drilled multilateral horizontal wells with water-based mud. The system consists of two upstream solid management systems, namely de-sander (cyclone), and sand catcher (filter). Downstream, the choke manifold, 4-phase separator, a downstream solid management equipment, and 3-phase separator are also included. Additionally, there is also a surge tank, as a backup flowback vessel to be used if needed to revive the well and offload any heavy fluids. This tank is used to initially help the well to gain the pressure momentum to naturally flow and offload heavy fluid present in production tubular. The cleanup campaign was successfully and safely completed for effective cleanup of more than 30 openhole horizontal multilateral wells without the use of any chemical treatments. The duration of cleanup operations was optimized using several techniques to effectively and efficiently remove existing mudcake. This paper provides the operational criteria to achieve effective and adequate mudcake removal for horizontal/multilateral wells and restore its optimal performance. Different design parameters and tailored flowback programs will be discussed, which led to effective drawdown pressure to reach optimized natural cleanup of each well. The well simulated flow model was also considered and used as input to design each well specific flowback program and minimize the risks of erosion, solids settlement in pipeline and downstream facilities. As a result, each well cleanup duration was reduced to an average of 1-2 day, while achieving the maximum potential production rate of each treated well.
This paper discusses the first Smart in-situ gas lift systems that were installed in three Saudi Arabia offshore wells. These Smart in-situ gas lift systems have proven to work in an offshore development environment for production enhancement. Implementation of this technology will extend the well life by allowing high water cut wells to produce, rather than become inactive, due to high hydrostatic back pressure in the wellbore. The selection of this system, which uses reservoir gas cap energy as compared to other artificial lift methods, resulted from economic considerations and operation simplicity in a non-electrified offshore field. The primary focus of this paper will be to discuss the first in-situ gas lift equipment, completion installation procedures, field test results, operation principles utilizing the gas cap energy, production strategy and well performance using an online monitoring system, and reservoir management considerations for future installations within the field. Initially, five conventional in-situ gas lift systems were installed in the field with problematic downhole sliding sleeve assemblies that required wireline intervention. As a result, Smart in-situ gas lift systems were recommended to allow auto opening of the downhole gas lift orifice valves from surface. These Smart systems have proven their durability over conventional systems, and will extend well life at a relatively higher water cut and maximize reservoir sweep efficiency. Introduction The Z-field is located in the Arabian Gulf and covers an area of approximately 20 km x 8 km. The main producing reservoir lies in an anticlinal trap with a northeast-southwest trending axis. The central part of the accumulation is overlain by a gas cap. As indicated by the cross-section shown in Fig. 1, the oil column consists of a massive, clean highly permeable (3–5 Darcy) sandstone unit overlain by 1–3 Darcy stringer sands interspersed with shales. The reservoir consists of sandstones, siltstones and shales with minor limestones and coals deposited in a complex, fluvial dominated delta system. The overlying gas cap is in direct communication with the stringer sands on the flanks of the anticline and with the Main sand in the central dome of the reservoir. Below the oil reservoir lies a strong aquifer that has maintained reservoir pressure over the past 10 years. The primary drive mechanism for the Main sand is from natural aquifer influx with limited support from gas cap expansion. The main driving mechanisms for the stringer sands is primarily gas cap, fluid and rock expansion, and moderate aquifer support at the flanks. Historically, all vertical wells have been free-flowing to the surface without any artificial lift method.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractWell bore cleanouts have been performed for many years with coiled tubing and it may be said that the cleanout operation is one of the most routine services performed in the coiled tubing industry; but until recently design was no more than a rule-ofthumb approach. Sufficient information is now available to facilitate informed decisions and achieve reliable engineering solutions, utilizing a sophisticated particle transport model.A methodical thought process, based on extensive research and mathematical modeling, will be presented for designing specific well bore cleanouts in a challenging offshore field in the Middle East. Case histories from a number of wells are documented detailing the conclusions from each. Laboratory analysis was performed on samples collected from the cleanout operations to further optimize and validate the design process. It is the intent of this paper to demonstrate the importance of sound engineering design, aided by comprehensive computer modeling technology.
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