Frac packing is a completion technique that merges two distinct processes-hydraulic fracturing and gravel packing. The main challenge of a frac-pack completion is the successful creation of high-conductivity fractures with the tip-screenout (TSO) technique and the placement of proppant within those fractures and in the annulus between the screen and wellbore wall. This is further compounded by having to do so in an ultra high-permeability environment, in which high fluid-leakoff rates are evident.From 1997 to 2006, job data from more than 600 frac-packing operations, representing an estimated 5% of the worldwide total, have been compiled into a database. This paper reviews well information and key frac-packing parameters. Also summarized are engineering implementations and challenges, best practices, and lessons learned. Essential frac-pack design parameters that were attained from the step-rate test (SRT) and minifrac test are evaluated. These include bottomhole pressure, rock-closure time, and fracturing-fluid efficiency. Downhole pressure and temperature are also discussed because of their importance to the post-completion efficiency evaluation and fracturing-fluid-optimization phase.Worldwide case histories are provided that demonstrate how to both deploy different frac-packing systems and pack the wellbore during extreme conditions with improved packing efficiency and a higher chance of success. Frac-Packing Downhole Tools and ProcedureDeepwater completions have constantly challenged placement design. Pumping rates have been increased to handle longer treatment intervals or to maximize proppant placement. Therefore,

A mechanical packer and abrasive perforator, conveyed by Coiled tubing(CT), grants great flexibility to the design of an annular fracturing treatment. On the downside the solids from a previous fracture treatment, or abrasive perforation cut, can be picked up by the subsequent pad fluid leading to a screen out. This is complicated by the fact that tolerance to solids varies between formations. To avoid this, solids transport during abrasive perforating, fracturing, displacement, and cleaning must be considered. Unique to this analysis is the ability to model the distribution of solids at any point in time, and the subsequent pick up of solids by the clean pad fluid. This leads to an unprecedented job optimization opportunity for reservoirs that can tolerate some solids in the initial pad stage, and risk mitigation for those which can’t. The model considers a transient mass balance for the solids bed and slurry. Non-uniform distribution of solids in the slurry is considered, which means the solids are not transported with the average slurry velocity. A drift flux model relates solids velocity in the slurry to the average slurry velocity. The difference between these is described by two terms. The first term accounts for variation in the cross sectional profiles of liquid velocity and solids concentration. This considers turbulent diffusion, settling velocity, and a liquid velocity profile based on Prandtl mixing length theory. The second term accounts for the interaction of gravity and buoyancy. Experiments to measure cleaning time involved a transparent pipe with a smaller pipe located eccentrically inside and a known amount of solids. Water is then injected through the smaller pipe and circulated in the annulus to clean the solids. The time required to remove all solids from the annulus is measured for a number of deviation angles and flow rates. Simulation results are compared to experimental data at all deviation angles. A field case is presented for a well that initially screened out during the pad after abrasive perforating. Finally a sample simulation details the solids transport for the entire process and a cleanout that was required following a screen out in the fracturing stage. This highlights how the model can be used to predict the axial distribution of solids in coiled tubing and wellbore at any time, for uphill and downhill flows, at all deviation angles.

Frac-packing is a completion technique that merges two distinct processes: Hydraulic fracturing and gravel packing. The main challenge of a frac-pack completion is the successful creation of high conductivity fractures using the tip-screen out technique and placement of proppant within those fractures and the annulus between the screen and wellbore. This is further compounded by having to do so in an ultra high permeability environment, where high fluid leak-off rates are evident. Since 1997, job data from more than 600 frac-packing operations worldwide have been compiled into a database. This paper reviews well information and key frac-packing parameters. Also summarized are engineering implementations and challenges, best practices, and lessons learned. Essential frac-pack design parameters attained from the step-rate-test (SRT) and mini-frac test are evaluated. These include bottom hole pressure, rock closure time and fracturing fluid efficiency. Down hole pressure and temperature are also discussed because of their importance to the post completion efficiency evaluation and fracturing fluid optimization phase. Worldwide case histories are provided demonstrating how to deploy different frac-packing systems and pack the wellbore under extreme conditions with improved packing efficiency and a higher chance of success.

More than 30% of coiled tubing (CT) operations worldwide are related to debris removal from a wellbore. The process is affected by multiple variables including fluid properties/velocities, particle properties, wellbore geometry and deviation, pipe size and eccentricity, fill penetration rate, and wiper trip speed. Debris cleanout with CT is challenged by the achievable pump rates and lack of pipe rotation. This challenge is further compounded by highly deviated or horizontal well trajectories, especially in large-diameter wellbores with low bottom-hole pressures. A hydraulically actuated, switchable circulation sub was developed a decade ago. While running into the well, forward jets of the sub help break down debris. While pulling out of the well, the tool is switched to a low resistance, backward jetting mode, which sweeps debris more efficiently using higher flow rates. However, in some challenging conditions such as compacted sand columns, or scale in extended wellbores, the sub has to be combined with other downhole tools to meet operational requirements. This paper discusses how to combine the switchable circulation sub with a tractor, water hammer tool, and a mud motor/bit. It goes on to demonstrate a means of verifying the tool is operated correctly using real time downhole signals transmitted by a small but robust conductor inside the CT. The benefits of this combination are multi-fold. First, while running into the well the tractor or water hammer tool helps to reach target depth. While pulling out of the well, the switchable circulation sub cuts off flow to the lower BHA (bottom hole assembly), stopping the bit/PDM (positive displacement motor) and/or idling the tractor or water hammer tool. At the same time, the flow rate can be increased with relatively lower surface injection pressures improving the hole-sweeping efficiency and pipe fatigue life. A few field case histories are presented to demonstrate the benefits of these special BHAs in improving operational efficiency. The challenges, benefits, and lessons learned during these operations are reviewed.

Transient gas-liquid flow is a common phenomenon in the drilling, workover and gas/oil production processes. Any change in the operating conditions at the inlet or outlet will introduce a transient response. Operations such as liquid unloading, under balanced drilling with gasified fluid, well control, cementing, hole cleaning, pipeline startup and blowout may never reach a steady state. In order to simulate the flow system, several transient two-phase flow simulators have been developed in the past. However, these models are based on the two-fluid model approach. They are complicated and time consuming to run since they treat the gas and liquid phase separately in terms of pressure, temperature and velocity. In this paper a new transient two-phase flow model has been developed. In each time step, the two-phase flow regime, liquid holdup and pressure gradient are estimated with the empirical correlations which are well developed for the steadystate flow. A drift-flux equation was introduced to close the system. The model was validated against data collected from the public literature, field operations, and other transient software. Several field cases are used to illustrate the transient nature of pipeline production, underbalanced drilling (UBD), sand cleanout, and liquid unloading. The benefits of using the transient simulation for the operational design, training and job execution are also discussed.