Erosion characteristics and simulation charts of sand fracturing casing perforation

Large-scale sand fracturing is a necessary means in the efficient exploitation of shale gas/oil.However,in the process of fracturing operation,the sand carrying fluid and proppant easily causes scouring and wear to production strings,especially the casing perforation system,which damage the wellbore integrity and deformation to affect the subsequent fracturing.For this problem,taking the actual construction conditions and perforation technology of an oilfield in western China as an example,the structural parameters of the downhole string were measured and the wall thickness reduction model of casing perforation suitable for large-displacement sand fracturing in horizontal well section was established.With software ANSYS-FLUENT,the casing perforation erosion under the conditions of different displacements,sand content and perforation sand-passing quantity in the process of sand fracturing was simulated and calculated.The influences of three parameters on perforation erosion and expansion were analyzed and the prediction chart of the influences of three main control factors on perforation erosion and expansion was established.The perforation erosion images after fracturing construction were obtained with the downhole eagle perforation logging technology.The logging chart results were compared with the downhole eagle perforation data.The error between the established numerical simulation calculation charts and the real logging data was about 5%,indicating that the simulation charts were the valuable reference.

Simulation of the erosion of casing and perforation under staged sand fracturing conditions in horizontal sections

The new fracturing technology of intensive stages and high-intensity proppant injection shows significant advantages of cost reduction and high efficiency in the volume fracturing of unconventional reservoirs,but it also intensifies the erosion of the casing and the perforations,with a perforation diameter expansion and the casing wall thinning.To solve this problem,in view of the applications of the perforation fracturing technology under the construction conditions in Mahu Area in Xinjiang,China,the structure parameters of the downhole strings are measured and a calculation model of the perforation casing erosion is established for the large-displacement sand fracturing process in horizontal sections.The software ANSYS-FLUENT is used to simulate the casing and perforation erosion under different conditions of the displacement,the sand content,the proppant particle size,and the fracturing fluid viscosity in the sand fracturing process.The particle size of the proppant and the viscosity of the fracturing fluid mainly affect the erosion area,but they have little influence on the erosion rate.The sand content and the displacement significantly affect the erosion rate.Among these factors,the sand content has a more significant effect on the erosion rate and the displacement has a more significant effect on the erosion area.Due to the influence of gravity,the perforation erosion rate is larger when the phase angle ranges from 120°to 240°.

Experimental modeling of sanding fracturing and conductivity of propped fractures in conglomerate:A case study of tight conglomerate of Mahu sag in Junggar Basin,NW China

True tri-axial sanding fracturing experiments are carried out on conglomerate samples from the Permian Wuerhe Formation of Mahu sag,Junggar Basin,to study hydraulic fracture propagation geometry and quartz sand transport in ma-trix-supported fine conglomerate and grain-supported medium conglomerate.The effect of rough fracture surface on conduc-tivity is analyzed using the 3D-printing technology to reconstruct the rough surface formed in the fractured conglomerate.The hydraulic fractures formed in the matrix-supported fine conglomerate are fairly straight,and only more tortuous when en-countering large gravels at local parts;thus,proppants can get into the fractures easily with transport distance about 70%–90%of the fracture length.By contrast,in the grain-supported medium conglomerate,hydraulic fractures tend to bypass the gravels to propagate in tortuous paths and frequently change in width;therefore,proppants are difficult to transport in these fractures and only move less than 30%of the fracture length.As the ma trix-supported fine conglomerate has high matrix content and low hardness,proppants embed in the fracture surface severely.In contrast,the grain-supported medium conglomerate has higher gravel content and hardness,so the quartz sand is crushed more severely.Under the high proppant concentration of 5 kg/m^(2),when the closure stress is increased(above 60 MPa),fractures formed in both matrix-supported fine conglomerate and grain-supported medium conglomerate decrease in width significantly,and drop 88%and 92%in conductivity respectively compared with the case under the low closure stress of 20 MPa.The field tests prove that under high closure stress above 60 MPa,using a high proportion of fine proppants with high concentration allow the proppant to move further in the fracture;meanwhile proppant places more uniformly in the ro ugh fracture,resulting in a higher fracture conductivity and an improved well per-formance.

Effect of reclaimed sand additions on mechanical properties and fracture behavior of furan no-bake resin sand

In this work, the effects of reclaimed sand additions on the microstructure characteristics, mechanical properties and fracture behavior of furan no-bake resin sand have been investigated systematically within the temperature range from 25 to 600 oC. The addition of 20%-100% reclaimed sand showed dramatic strength deterioration effect at the same temperature, which is associated with the formation of bonding bridges. Both the ultimate tensile strength(UTS) and compressive strength(CS) of the moulding sand initially increase with the increase of temperature, and then sharply decrease with the further increase of temperature, which is attributed to the thermal decomposition of furan resin. The addition amount of reclaimed sand has a remarkable effect on the room temperature fracture mode, i.e., with the addition of 0-20% reclaimed sand, the fracture mode was mainly cohesive fracture; the fracture mode converts to be mixture fracture mode as the addition of reclaimed sand increases to 35%-70%; further increasing the addition to 100% results in the fracture mode of typical adhesive fracture. The fracture surface of the bonding bridge changes from a semblance of cotton or holes to smooth with the increase of test temperature.

A laboratory study of hot WAG injection into fractured and conventional sand packs

Gas injection is the second largest enhanced oil recovery process, next only to the thermal method used in heavy oil fields. To increase the extent of the reservoir contacted by the injected gas, the gas is generally injected intermittently with water. This mode of injection is called water-alternating-gas (WAG). This study deals with a new immiscible water alternating gas (IWAG) EOR technique, “hot IWAG” which includes combination of thermal, solvent and sweep techniques. In the proposed method CO2 will be superheated above the reservoir temperature and instead of normal temperature water, hot water will be used. Hot CO2 and hot water will be alternatively injected into the sand packs. A laboratory test was conducted on the fractured and conventional sand packs. Slugs of water and CO2 with a low and constant rate were injected into the sand packs alternatively; slug size was 0.05 PV. Recovery from each sand pack was monitored and after that hot water and hot CO2 were injected alternatively under the same conditions and increased oil recovery from each sand pack and breakthrough were measured. Experimental results showed that the injection of hot WAG could significantly recover residual oil after WAG injection in conventional and fractured sand packs.