Jean Desroches

Can We Engineer Better Multistage Horizontal Completions? Evidence of the Importance of Near-Wellbore Fracture Geometry From Theory, Lab and Field Experiments

Note: SPE 173363 Reference EPFL-CONF-212843 Record created on 2015-10-08, modified on 2016-08-09

Are Preflushes Really Contributing to Mud Displacement During Primary Cementing

During a primary cementing operation, it is most of the time necessary to prevent direct contact between the drilling mud and the cement slurry that is to be placed in the wellbore. The reason is that these two fluids are usually incompatible. This incompatibility can manifest itself either as an accelerating effect, the drilling mud/cement mixtures having a shorter thickening time than the cement itself, which is obviously not acceptable, or as a viscosifying effect, the drilling mud/cement mixtures being more or much more viscous than any of the two uncontaminated fluids, which can be detrimental to the displacement process.

Experiments versus theory for the initiation and propagation of radial hydraulic fractures in low‐permeability materials

We compare numerical predictions of the initiation and propagation of radial fluid-driven fractures with laboratory experiments performed in different low permeability materials (PMMA, cement). In particular, we choose experiments where the time evolution of several quantities (fracture width, radius, wellbore pressure) were accurately measured and for which the material and injection parameters were known precisely. Via a dimensional analysis, we discuss in detail the different physical phenomena governing the initiation and early stage of growth of radial hydraulic fractures from a notched wellbore. The scaling analysis notably clarifies the occurence of different regimes of propagation depending on the injection rate, system compliance, material parameters, wellbore and initial notch sizes. In particular, the comparisons presented here provide a clear evidence of the difference between the wellbore pressure at which a fracture initiates and the maximum pressure recorded during a test (also known as the breakdown pressure). The scaling analysis identifies the dimensionless numbers governing the strong fluid-solid effects at the early stage of growth, which are responsible for the continuous increase of the wellbore pressure after the initiation of the fracture. Our analysis provides a simple way to quantify these early time effects for any given laboratory or field configuration. The good agreement between theoretical predictions and experiments also validates the current state of the art hydraulic fracture mechanics models, at least for the simple fracture geometry investigated here.

Robustness to formation geological heterogeneities of the limited entry technique for multi-stage fracturing of horizontal wells

Robustness to formation geological heterogeneities of the limited entry technique for multi-stage fracturing of horizontal wells is investigated. It is necessary to simulate the complete process of initiation and propagation of multiple hydraulic fractures, accounting for fluid flow in the wellbore together with perforation friction and stress interaction between fractures, to fully investigate the robustness of the limited entry technique. A newly developed model is used for accounting for all these features, assuming that all fractures remain radial, transverse to the wellbore. The simulations carried out are focused on fracture initiation and radial propagation to provide insight into the initial and crucial stage of fracture growth before proppant is injected into the fractures.

CO2 Storage Geomechanics for Performance and Risk Management

Note: SPE 108528 Reference EPFL-CONF-212823 Record created on 2015-10-08, modified on 2016-08-09

Flow of viscoplastic suspensions in a hydraulic fracture: implications to overflush

The study is devoted to modeling of multiphase flows of immiscible viscoplastic fluids in a hydraulic fracture. In the framework of the lubrication approximation, three-dimensional Navier-Stokes equations are reduced to hyperbolic transport equations for the fluid tracers and a quasi-linear elliptic equation in terms of the fluid pressure. The governing equations are solved numerically using the finite-difference approach. A parametric study of the displacement of Bingham fluids in a Hele-Shaw cell is carried out. It is found that fingers developed through the pillar of a yield-stress suspension trigger the development of unyielded zones. An increase in the Bingham number leads to an increase in the so-called finger shielding effect, which manifests itself via an increase in the overall finger penetration zone and a decrease in the total number of fingers. The effect of flow parameters on the displacement of hydraulic fracturing proppant-laden suspension by a clean fluid in the vicinity of the perforation zone is carried out. This particular case is considered in application to overflush at the end of a stimulation treatment, when a small portion of a thin clean fluid is injected to wash out the particles from the wellbore into the fracture. It is found that an increase in the yield stress and the viscosity contrast between the fracturing and the overflush fluids typically reduces the area of the cavity thus mitigating the risk of loosing the conductive path between the wellbore and the fracture after the fracture closure.

Geomechanical Drivers of the (in)-Efficiencies of Multi-stage Hydraulic Fracturing

We discuss the impact of in-situ stress variations and near-wellbore geomechanical complexity on the efficiency of simultaneously initiating and propagating hydraulic fractures from a horizontal well. Such a multi-stage hydraulic fracturing technique is used routinely in the development of unconventional reservoirs in order to reduce operations costs. However, the resulting production rate from the different fractures along the well has been found to vary widely for a large number of different reservoirs. We show by numerical modeling of the multi-stage fracturing process that it is extremely difficult to properly balance the flow rate entering the different fractures stimulated at once during a pumping stage. It results that some fractures not only propagate further than others but also receive more proppant, both of which ultimately impacting the production rate of each fracture. Based on numerical modeling and field evidence, we argue that the reasons for such a poor efficiency of the fluid partitioning can be related to heterogeneities in both the in-situ stress field and the tortuous near-wellbore fracture path.

Rock Fabric Influence on Hydraulic Fracture Propagation

Hydraulic fracturing is crucial for hydrocarbon production from unconventional reservoirs. However, often the efficiency of the completion treatment is poor, which is considered to be a result of lateral heterogeneity in reservoir quality. To investigate the influence of rock fabric on a near-wellbore geometry, we conducted two laboratory tests on Niobrara outcrop shale blocks stressed in true-triaxial frames. The Acoustic Emission (AE) technique monitored hydraulic fracture initiation and propagation, while post-test measurements revealed the fracture shape and aperture. In both tests, AE analysis indicated hydraulic fracture initiation prior to the maximum wellbore pressure (breakdown) and asymmetrical fracture propagation. Post-test analysis demonstrated that AE results corresponded well with post-mortem surface maps. The first test revealed a crossing of weak bedding planes accompanied by fluid leak-off. In the second test, the hydraulic fracture was arrested at the boundary of a calcite-filled fracture. In addition, fracture aperture mapping indicated narrow aperture in that area. We conclude that near-wellbore planes of weakness, such as mineralized natural fractures, can result in hydraulic fracture propagation arrest, or in poor fracture geometries with limited aperture that, in turn, could lead to high treating pressures, low fracture conductivity, restricted proppant delivery and decreased production.