Development of unconventional reservoirs in North America has increased significantly over the past decade. The increased activity in this space has provided significant data with respect to through-tubing drillouts which had previously not been attainable. This paper is focused on using the field data from the Montney and Duvernay formations along with laboratory data and numerical modeling to understand the hole cleanout associated with through-tubing drillouts of frac plugs. Initially, an extensive full-scale flow loop laboratory testing program was conducted to obtain data on debris transportation for hole cleanout during through-tubing applications. The testing was conducted on various coiled tubing (CT)-production tubing configurations using various solid particles. The laboratory data was used to develop empirical correlations needed for a transient debris transport model. This model was then used for frac plug drillouts to ensure successful hole cleaning in actual field applications. Computational fluid dynamics (CFD) modelling was also used to further understand and quantify the differences between the laboratory data, field data and transient debris transport model results. The objective of the work conducted was to gain a better understanding of debris transport and validate the empirical modelling approach developed for hole cleaning. The validation process was conducted in several stages. The first stage was to validate the laboratory data against the Montney and Duvernay field data. The second stage was to verify the results obtained from the empirical model against the results obtained from a computational fluid dynamic model. The results from both modelling approaches were lastly compared to the field data. All these results challenge the current industry's understanding and best practices for through-tubing drillouts in the Montney and Duvernay formations. With the contentious increase of lateral lengths and higher stage counts, the process of drilling out frac plugs has become more complex. This study explicitly benefits all operators in their ever-increasing need to understand their frac plug drillout operations to ensure efficient, cost effective, and most importantly, consistent and repeatable results. While efficient results for frac plug drillout operations have been accomplished to date, the on-going feedback from the field has been the requirement to produce repeatable drillouts. This paper is the first to show a holistic approach for obtaining a transient debris transport model used for through-tubing drillouts of frac plugs. The novelty also consists of the transient debris transport model validation through laboratory data and actual Montney and Duvernay field data.
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.
Concentric Coiled Tubing Vacuum Technology (CCTVT) was developed in the mid 1990s in Canada, and since then has spread worldwide. The technology was initially focused on sand cleanouts in heavy-oil, low-pressure, deviated wells, where other cleanout methods, including conventional CT interventions, were inefficient. Under such conditions, CCTVT provided a simple but very effective solution.In general terms, the technology comprises a downhole jet pump run on a concentric coiled tubing (CCT), which is a coiled tubing string inside another coiled tubing string. A single-phase fluid is pumped through the inner string to power the downhole jet pump, creating a localized drawdown that vacuums well fill (fluids and/or solids), increases the return pressure, and circulates fluids and solids back to surface via the CCT annulus.Since the introduction of this technology, it has gone through several updates in order to face new challenges. The latest BHA versions include multiple operational modes to improve cleanout efficiency, minimize runs, function with supplementary tools and most recently, to accommodate a specialized electric conductor to run a real-time logging tool in conjunction with the jet pump.Currently, the application of the system has extended beyond solids removal on heavy oil, onshore wells. The current work scope ranges from very simple operations such as drilling fluid and filter cake removal, liquid unloading, inflow profiling, evaluating completion integrity, matrix stimulation, pressure and temperature logging, etc.; to more complex and challenging operations such as memory production logging, H 2 S inhibition, multilateral wells, chemical sand consolidation, hydrate removal and realtime production logging. These operations are occurring in the full range of oilfield locations: onshore and offshore wells, from fixed installations to mobile rigs, in jungle to arctic conditions. This paper will summarize the new techniques that are being applied in many global locations with CCTVT. Each technique will be illustrated with case histories detailing time and cost savings and, where relevant, production improvements.
This paper will present an update on the operational benefits of utilizing anti-cracking inhibitors in sour wells. Multiple papers have shared the details of a Joint Industry Project which resulted in a one-size-fits-all fatigue derating factor by the service supplier. In recent years, additional testing has challenged that practice and a greater variety of improved derating factors are utilized in fatigue tracking software. The testing process of exposing samples to sour conditions for 72 hours and conducting bend fatigue testing post exposure remains the method used in this paper. The process updated the JIP practice of one-time coating of the sample with the addition of an anti-cracking inhibitor to the sour fluid. This update more closely replicates real-world operations. In addition, there was a greater focus on the test sample size, stress and strain to reduce fatigue testing time and reduce the effects of any outgassing leading to a more accurate and repeatable test. A comparison of three typical test methods will be presented: non-inhibited sour tests by the original equipment manufacturer, inhibited field specific partial pressure testing by an operator and globally applicable inhibited testing conducted at the maximum apparatus test level by a service provider. Comparison of prior anti-cracking inhibitor and a North Sea approved inhibitor results will be detailed. The practice for conducting the tests with a high yield material and extending the results to a lower grade material with similar chemistry will be detailed. Note that the results of separate tests conducted on the pipe body and bias welds will be compared and detailed. A brief summary of the service providers record of global sour pipe operations will illustrate these practices have proved suitable in the field. The updated practices and procedures for sour testing have not been shared in prior papers. The improved pipe life will assist the industry with efficient and safe operational planning in sour wells. Finally extending pipe life will reduce the amount of raw steel required for operations and ultimately reducing carbon dioxide emissions, a global challenge from which we can all benefit.
Acid-tunneling is an acid jetting method for stimulating carbonate reservoirs. Several case histories from around the world were presented in the past showing optimistic post-stimulation production increases in open-hole wells, comparing to conventional coiled tubing (CT) acid jetting, matrix acidizing, and acid fracturing. However, many questions about the actual tunnel creation and tunneling efficiency are still not answered. In this paper, the results of an innovative full-scale research program involving water and acid jetting are reported for the first time. The tunnels are constructed through chemical reaction and mechanical erosion by pumping hydrochloric (HCl) acid through conventional CT and a bottom-hole assembly (BHA) with jetting nozzles and two pressure-activated bending joints that control the tunnel initiation directions. If the jetting speed is too high and the acid is not consumed in front of the BHA during the main tunneling process, then unspent acid flows toward the back of the BHA and creates main wellbore and tunnel enlargement with potential wormholes as fluid leaks off, lowering the tunneling length efficiency. Full-scale water and acid jetting tests were performed on Indiana limestone cores with 2-4 mD permeability and 12-14% porosity. Many field-realistic combinations of nozzle sizes, jetting speeds, and back pressures were included in the testing program. The cores were 3.75-in. in diameter by 6-in. in length for the water tests, and 12-in. in diameter by 18-in. in length for the tests with 15-wt% HCl acid. The jetting BHA was moved as the tunnels were constructed, at constant force on the nozzle mole, to minimize the nozzle stand-off distance. Six acid tests were performed at the ambient temperature of 46F and two at 97F. The results from the acid tests show that the acid tunneling efficiency can be optimized by reducing the nozzle size and pump rate. The results from the water and acid tests with exactly the same parameters to match the actual CT operations in the field show that the tunnels are constructed mostly by chemical reaction and not by mechanical erosion. The acid tunneling efficiencies obtained from the full-scale acid tests are superior to the average tunneling efficiency of more than 500 actual tunnels constructed during more than 100 acid tunneling operations performed to date worldwide. The paper describes the full-scale water and acid jetting tests on Indiana limestone cores. The major novelty of this test program consists of performing all measurements with back pressure, unlike all previous water and acid jetting studies reported in literature, to more accurately mimic the downhole well conditions. The novel understanding of the combined effect of the nozzle size, pump rate, and back pressure significantly improves the actual acid-tunneling efficiency.
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