As the quest for new petroleum supplies has increased in the past few years, operators have been forced to drill deeper to find new reserves. Much of the higher cost of drilling deeper, especially onshore, is typically associated with decreased rate of penetration (ROP) caused by both harder rock and higher mud weights required to counter the overpressured reservoirs often associated with deeper drilling. The following discussion centers on technologies intended to enhance the deep drilling capability. Industrial hammers for hard rock drilling have been around for some time, but most have been air operated and used in the mining industry. Historically, hammers have been thought to have limited capability in oil and gas drilling operations, with their use limited to air drilling.
Ma, Xiang (ExxonMobil Upstream Research Company) | Zhou, Fuping (ExxonMobil Upstream Research Company) | Ortega Andrade, Jose Alberto (ExxonMobil Upstream Research Company) | Gosavi, Shekhar (ExxonMobil Upstream Research Company) | Burch, Damian (ExxonMobil Upstream Research Company)
Hydraulic fracturing has revolutionized shale oil/gas production in the last decades, but further robust understanding is needed as to what happens during fracture placement. At the end of the pumping process, the sudden change in pump rate leads to a pressure fluctuation in the wellbore referred to as water hammer. These pressure pulses could contain useful information about the generated fractures and their geometry. Our study focused on a detailed look of water hammer signatures on the time-domain as a diagnostic tool for hydraulic fracture geometry. Our water hammer model extends on current industry known formulations. The model solves the fluid transient equation and treats the hydraulic fracture as the boundary condition. We propose a new way to derive the fracture boundary condition based on an improved description of the physics downhole. The model includes pressure-dependent leak-off and perforation friction which are key to determine fracture growth and near wellbore tortuosity. The boundary condition is derived through the fracture entry friction equation instead of previous attempts to use an electrical-circuit analogous system. By changing the input fracture dimensions of the model, we are able to simulate different pressure fluctuations at the wellhead. A novel workflow was also developed to link fracture dimensions to the observed field data. It utilizes an iterative ensemble smoother algorithm to solve the resulting optimization problem. The results and trends obtained with the new water hammer model were validated using well data from the Permian basin. The model validation effort showed and characterized the non-uniqueness of simulation outcomes. We considered several cases of input parameters in order to probe the parameter space of water hammer interpretations. The range of fracture geometry predictions for a particular stage was shown to be broad despite reasonable matches of the water hammer waveform. It proved challenging to find patterns for refining input ranges without converging to widely different fracture geometries. The simulated pressure losses associated the fracture geometry prediction were not consistent in some instances with engineering understanding. A potential source for the characterized non-uniqueness of water hammer simulation outcomes is the inability of time-domain methodologies to generate an appropriate number of physical relations to resolve the physically meaningful variables of interest (fracture length/height/width). In addition, the use of low-frequency water hammer waveforms may not embody the information necessary to resolve hydraulic fracture features. Based on our results and observations, the non-uniqueness of the solution space does not allow us to effectively use the time-domain water hammer interpretation as a diagnostic tool for hydraulic fracture geometry.
Li, Bodong (Drilling Technology Division, EXPEC Advanced Research Center) | Zhan, Guodong David (Drilling Technology Division, EXPEC Advanced Research Center) | Suo, Zhongwei (SINOPEC Research Institute of Petroleum Engineering) | Sun, Mingguang (SINOPEC Research Institute of Petroleum Engineering)
This paper introduces the hydro-efflux hammer - a rotary percussion drilling tool that is developed to improve ROPs in hard and abrasive formations. Hydro-efflux hammer is a hydro-mechanical tool which utilizes drilling fluid to power its continuous percussion motion. The tool's rock-breaking capability is achieved by the high unit load and unique breaking methods. The periodic impact generated by the tool excites strong pulsating stress waves, which strengthens the concentrated stress in internal rocks, and speeds up the rock breaking process. For the design of the tool, improved system integrity is achieve by implementing optimized actuating mechanism, sealing components, and anticorrosion materials. The optimization also involves fine tuning the tool including its percussion stroke and impact energy based on the formation characteristics. Recent field test results in challenging formations are presented and analyzed. In this work, based on the testing result, a number of approaches to extend the life time of the tool for higher performances are also proposed.
Water hammer shock pulses are generated when the flow in a length of tubing is interrupted in a time that is much shorter than the pulse duration. Water hammer tools used for well intervention incorporate a poppet valve that closes very quickly and a pilot valve that then causes the valve to open so that the flow is stopped periodically. The upstream water hammer shock generates an impulsive mechanical load on the bottom hole assembly (BHA) that can be used for milling or other applications. The intense axial vibration also extends the reach of tubing in long tortuous completions. These tools also generate a significant rarefaction shock downstream of the tool, comprising a sudden drop in pressure that can extend over 100's of meters of wellbore. The rarefaction pulse propagates into the dead volume beneath the tool and upstream into the annulus. The rarefaction shock causes flow to surge into and out of the formation. The extent and duration of these pulses has been observed in surface tests. Case histories of well cleaning and stimulation applications are described. Best practices for operation include squeezing treatment fluids into the formation followed by flow circulation to shock surge the completions.
Drilling the Severnaya Truba field in Aktobe, Kazakhstan, has been costly and time consuming. The mechanical lifting and falling action creates a rapid variation in weight on bit (WOB), allowing the bit's DOC to fluctuate while overcoming different stresses. These variations, along with the percussion pulse created with each stroke, led to increased rates of penetration (ROPs). Drilling with an air hammer is a technique whereby gases (typically compressed air or nitrogen) are used to operate a pneumatic hammer, to cool the drill bit, and to lift cuttings out of the wellbore. Air forced down the drillstring actuates the percussion tool, which, in turn, creates an axial percussion force directed down to a specially designed drill bit.
While rising oil prices are offering short-term relief for stressed oil company executives, in the long term their companies could be dead. US production was up by more than 1 million bbl last year. But Dave Pursell, managing director for investment banking in energy technology for Tudor, Pickering, and Holt, said there are cracks showing in the industry's long-term technology solution: hammering longer wells with ever more fluid and sand. If you are an oil and gas producer, you better be employing technology" if you hope to be around for the long term. Growth is getting harder to come by.
ABSTRACT: This paper presents an objective review of two non-destructive methods developed for the rapid and cost-effective testing of compressive strength on rock cores. Rebound impact test and scratch test methods are compared. Respective advantages and drawbacks are listed in terms of the following aspects: (i) sample preparation, (ii) destructivity, (iii) repeatability, (iv) resolution, (v) natural bias, (vi) sensitivity to sample size and, (vii) lithology dependence of the correlation between test results and rock strength. Discussions of these points are illustrated with examples from a large data base consisting of sets of Leeb hardness values and scratch strength collected on core samples from different formations including sandstones, carbonates and shales from various regions around the globe.
As a primary input for many standard geomechanical models, rock strength is routinely measured on rock samples used in basic core analysis programs for geomechanics. Rock Strength is traditionally assessed as the Uniaxial Compressive Strength (UCS) measured during the axial loading and crushing of cylindrical samples (“plugs”) extracted from cores. Even though this test is widely accepted as a standard index test for rock strength assessment, its methodology suffers from the following limitations: (I) sample preparation requirements: conventional strength testing methods are not concerned with whole core sections but rather with cylindrical samples which must be prepared specially for these tests according to stringent specifications and dimensional controls; (II) destructivity: samples can only be tested once as they are destroyed in the process; (III) natural dispersion: the test interpretation for interparticular strength rely on the occurrence of a specific type of failure along shear planes inclined with respect to the cylindrical sample axis, yet only a fraction of samples fail this way. Natural defects and heterogeneity in tested samples often leads to different failure behaviors, thereby invalidating the test interpretation; (IV) discrete measurements: strength tests run on plug samples are only concerned with a limited fraction of the core volume and sometimes omit representative lithologies or even facies from the testing program, (V) natural bias: plug samples may be hard to get from soft, unconsolidated materials, which may result in a bias of the test results toward the stronger core sections, leaving the weaker intervals underrepresented or poorly sampled.
Lin, Y. X. (State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Effective Development) | Wei, S. M. (China University of Petroleum) | Zeng, Y. J. (Sinopec Engineering Technology Research Institute) | Gao, S. Y. (Sinopec Engineering Technology Research Institute) | Jin, Y. (China University of Petroleum) | Lu, Y. H. (China University of Petroleum) | Li, Z. J. (China University of Petroleum)
ABSTRACT: The dynamic pore pressure increases once the impact load is applied to the rock surface. Based on the theory of poroelasticity, the analytical solution of the pore pressure induced by the impact load is obtained. When an impact load is applied onto the surface of the bottom rock, the pore pressure in the computational domain reaches its peak in a very short time, and then decreases rapidly. The amplitude of the pore pressure keeps increasing along with a larger impact load applied onto the downhole surface. The results show that the smaller the Poisson's ratio is, the higher the pore pressure will be. The elastic modulus and porosity have the same effects on the bottom rock. The higher the permeability of the rock, the faster the pore pressure drops down, which recommends an impact load with higher frequency. This study is instructive for understanding the variation of rock properties at bottom hole when the impact load is applied, and also for optimizing the design of rotary percussion drilling tools and their serviceable range.
Hydraulic axial impactor is driven by high-pressure fluid, which is convenient for drilling in deep wells and hard rocks. Therefore, it has once again become a popular research topic all over the world in recent years. The application of hydrodynamic axial percussion drilling has been proposed since one hundred years ago. As early as 1887, Wolf Bushmann, a German, proposed the idea of using liquid energy to drive hydrodynamic hammers to achieve hydraulic axial impact. After that, the technology of hydraulic axial impact rotary drilling has been widely used in drilling and has achieved great success.
Finger (1984) found a way to improve the penetration rate by applying hydraulic hammer into the standard air drilling rig (Finger. 1984). Later on, a percussion drill bit had been used in mining drilling, which dramatically increased the speed of air drilling. Samuel (1996) introduced the unit footage cost and drilling efficiency of downhole mud impact hammer (Samuel. 1996). Santos et al. (2000) believed that reducing costs during drilling of hard formations had become an important constraint in the modern exploitation of oil and gas fields, and it's urgent to develop a new drilling tool to reduce the high cost of hard rock penetration (Santos et al. 2000). Jian and Shang (2005) proposed a new type of rotary drilling tool with controlled mud hammer, which is aimed at increasing the rate of penetration, especially in deep hard formations (Jian and Shang. 2005). David Harris et al. (2010) studied the hydrodynamic axial impact in marine drilling and applied hydraulic hammers to conduct marine drilling at a depth of 155m in eastern Canada, thereby greatly improving the efficiency of offshore drilling (Harris et al. 2010).