Summary As part of an Equinor technical efficiency program that was initiated in 2015 to deliver savings and improvements, bridging particles were removed from the drilling fluids of 15 wells in Oseberg Main and instead loss control material (LCM) was used, as required, in some but not all the wells. These long, horizontal wells were a combination of open hole (OH) and sand screens with and without inflow control together with cased and perforated (C&P) completions, producing from typical Brent Group sandstone formations with permeabilities varying from approximately 10 md to darcy sandstones, and which were depleted by as much as approximately 280 bars. In 2018, an extensive study was performed on these wells to determine the impact on inflow performance of drilling without bridging particles. It was realized that the 15 wells offered a worst-case scenario to study in the field rather than laboratory the significance of formation damage on well productivity. The data set generated offered a unique opportunity to challenge conventional formation damage assertions, especially for long, horizontal wells. The influence of different parameters, including LCMs, lower completion design, loss type, mud penetration depth, dynamic overbalance while drilling, length of production interval, net to gross (NTG) and kh were considered for those wells drilled without bridging particles. One of the surprising findings was that there was no clear evidence that losses were detrimental to the productivity of these long horizontal wells; i.e., it would appear that the Brent reservoir sections, despite being depleted, were more resistant to the influence of formation damage on inflow performance than first thought. Furthermore, for this example bridging particles appear to be of less importance in the avoidance of formation damage but are important in preventing excessive increases in fluid costs due to losses. After a thorough review of all the data obtained from this study, together with the conclusions drawn, it was realized that these had direct implications for Equinor's approach to fluid qualification, and especially coreflooding. The most important conclusion that influenced this change in approach was that the long reservoir sections (approximately 1 km or more) within typical Brent heterogeneous formations appear to tolerate more formation damage without impairing the productivity index (PI). A direct consequence of this was the conclusion that more emphasis should be placed on fluid compatibility, mobility, screen plugging and stability along with particle-size distribution (PSD) design, while the importance of coreflooding to fluid qualification was downgraded for Brent and reservoirs of similar characteristics. This is not to say that coreflooding will not be performed, but rather it will be targeted toward situations where the influence of formation damage on well productivity is more significant; e.g., high-pressure and high-temperature fields where special drilling and completion fluids are required, low-permeability formations without mechanical stimulation, and shallow reservoirs with low reservoir temperature. In this paper, we will perform an evaluation of the significance of formation damage on well productivity and use this to demonstrate Equinor's revised approach to formation damage laboratory evaluation based on field experiences.

In this paper, we describe a simulation model for computing the damage imposed on the formation during overbalanced drilling. The main parts modeled are filter-cake buildup under both static and dynamic conditions; fluid loss to the formation; transport of solids and polymers inside the formation, including effects of porelining retention and pore-throat plugging; and salinity effects on fines stability and clay swelling. The developed model can handle multicomponent water-based-mud systems at both the core scale (linear model) and the field scale (2D radial model). Among the computed results are fluid loss vs. time, internal damage distribution, and productivity calculations for both the entire well and individual sections.The simulation model works, in part, independently of fluidloss experiments (e.g., the model does not use fluid-leakoff coefficients but instead computes the filter-cake buildup and its flow resistance from properties ascribed to the individual components in the mud). Some of these properties can be measured directly, such as particle-size distribution of solids, effect of polymers on fluid viscosity, and formation permeability and porosity. Other properties, which must be determined by tuning the results of the numerical model against fluid-loss experiments, are still assumed to be rather case independent, and, once determined, they can be used in simulations at altered conditions as well as with different mud formulations. A detailed description of the filter-cake model is given in this paper.We present simulations of several static and dynamic fluidloss experiments. The particle-transport model is used to simulate a dilute particle-injection experiment taken from the literature. Finally, we demonstrate the model's applicability at the field scale and present computational results from an actual well drilled in the North Sea. These results are analyzed, and it is concluded that the potential effects of the mechanistic modeling approach used are (a) increased understanding of damage mechanisms, (b) improved design of experiments used in the selection process, and (c) better predictions at the well scale. This allows for a more-efficient and more-realistic prescreening of drilling fluids than traditional core-plug testing. September 2010 SPE Journal Simulation ModelThis section describes the various modules that constitute the newly developed simulation model. The two main parts of the Maximize program are (1) the filter-cake model handling filter-cake buildup and controlling flow into the formation and (2) the reservoir-flow model handling flow inside the formation. The fluids introduced to the formation contain a number of dissolved and dispersed components, which, in turn, may change the original flow properties of the formation through various chemical and physical processes. The retention of solids and polymer is split into a pore-throat-trapping model and a pore-lining-adsorption model. Brine interaction with the rock surface and clays is described by a multicomponent cation-exchange mod...

Summary Formation damage has received significant attention over many years as one of the primary reasons for well productivity impairment, to the detriment of completion damage. The objective of this paper is to redress this imbalance and to focus on the significant contribution that completion damage has on well productivity. Formation damage is a reduction in inflow performance because of damage to the near wellbore, while completion damage is an increased pressure drop affecting the lower completion (e.g., plugging of sand screens and frac-packs). A completion damage classification system is presented for the first time that relates this damage type to the typical lower completion designs used by Equinor throughout well lifetime. In addition, a review of some of the fluid qualification tests involving completion damage either directly or indirectly has been performed to assess how representative these are. Computational fluid dynamics (CFD) was identified as a useful tool to assess how representative testing was. Fluid compatibility. CFD was used to determine the displacement efficiency from drilling to completion fluid in a candidate well, and hence the mixing ratio of drilling fluid to completion fluid to be used in compatibility tests. Furthermore, CFD simulations provided an indication of the likely shear rates occurring during displacement that were later used in the testing. Fluid stability. To determine the influence of sag on fluid displacement efficiency, CFD was used to model the worst-case situation where all the weighting agents came out of suspension. Using the displacement efficiency and shear rates obtained, a new dynamic completion damage test was devised to determine the potential for screen plugging as this is the most common lower completion used by Equinor. This test uses the same equipment as coreflooding except that the plug is removed, and a screen is inserted. Finally, an overview will be presented with recommendations of how Equinor’s approach to completion damage has changed because of this study, with an increased focus on achieving a better balance in the evaluation of formation and completion damage prior to the drilling and completion of wells.

Summary There are two types of sand-retention tests (SRTs) generally used in the industry to evaluate the performance of sand-control screens for standalone-screen (SAS) applications—prepack tests and slurry tests. They represent complete hole collapse and gradual rock failure around the wellbore, respectively. In this paper, we present analytical models and Monte Carlo (MC) simulations to estimate sand production in slurry-type SRTs with square-mesh screens while taking into account the full particle-size distribution (PSD) of the formation sand. We also compare the model results with four sets of experimental data and demonstrate that this approach can be used to predict sand production for different sand-size-distribution/screen-size combinations without the need for physical tests (provided that both an accurate representation of the formation-sand PSD and an accurate representation of screen pore sizes are available). This work augments previously published slurry-test models that were limited to wire-wrapped screens (WWSs), and enables the comparison of the performance of square-mesh screens with WWSs. The analytical model and the MC simulations provide a direct and reliable way to estimate the amount of sand that will be produced for a given sand-size distribution and a given screen size. Because the proposed methods are much more quantitative, they represent a significant improvement that surpasses current methods that rely on single design points or rules of thumb for screen selection.

As part of an Equinor technical efficiency programme that was initiated in 2015 to deliver savings and improvements, bridging particles were removed from the drilling fluids of 15 wells on Oseberg Main and instead loss control material (LCM) was used, as required, in some but not all the wells. These long, horizontal wells were a combination of open hole (OH) and sand screens with and without inflow control together with cased & perforated (C&P) completions, producing from typical Brent Group sandstone formations with permeabilities varying from approximately 10 mD to Darcy sands, and which were depleted by as much as approximately 280 bars. In 2018, an extensive study was performed on these wells to determine the impact on inflow performance of drilling without bridging particles. It was realized that the 15 wells offered a worst-case scenario to study in the field rather than laboratory the significance of formation damage on well productivity. The data set generated offered a unique opportunity to challenge conventional formation damage assertions, especially for long, horizontal wells, examples of which are as follows. Formation damage reduces productivity Significant mud losses with deep penetration lead to wells with lower than expected inflow performance Bridging particles are required to prevent formation damage around the near wellbore Drilling through heavily depleted reservoirs will result in severe formation damage Excessive use of graphite in an OH reservoir section will reduce inflow performance The influence of different parameters, including loss control materials, lower completion design, loss type, mud penetration depth, dynamic overbalance while drilling, length of production interval, net to gross (NTG) and kh were considered for those wells drilled without bridging particles. One of the surprising findings was that there was no clear evidence that losses were detrimental to the productivity of these long horizontal wells, i.e. it would appear that the Brent reservoir sections, despite being depleted, were more resistant to the influence of formation damage on inflow performance than first thought. Furthermore, for this example bridging particles appear to be of less importance in the avoidance of formation damage but are important in preventing excessive increases in fluid costs due to losses. After a thorough review of all the data obtained from this study, together with the conclusions drawn, it was realized that these had direct implications for Equinor's approach to fluid qualification, and especially coreflooding. The most important conclusion that influenced this change in approach was that the long reservoir sections (approximately 1 km or more) within typical Brent heterogeneous formations appear to tolerate more formation damage without impairing the productivity index (PI). A direct consequence of this was the conclusion that more emphasis should be placed on fluid compatibility, mobility, screen plugging and stability along with particle size distribution (PSD) design while the importance of coreflooding to fluid qualification was downgraded for Brent and reservoirs of similar chacteristics. This is not to say that coreflooding will not be performed, but rather it will be targeted towards situations where the influence of formation damage on well productivity is more significant, e.g. HTHP fields where special drilling and completion fluids are required, low permeable formations without mechanical stimulation, and shallow reservoirs with low reservoir temperature. This paper will perform an evaluation of the significance of formation damage on well productivity and use this to demonstrate Equinor's revised approach to formation damage laboratory evaluation based upon field experiences.