Proppant selection

Proppant selection
Determine proppant type, particle size and concentration were laid in cracks (or arrange layers) are an important part of fracturing design, but also to ensure after pressure increase and improve the level of development (production rate increase, the increase in recoverable reserves ) key. In general, is expected to obtain the desired effect of fracturing selected proppant fracture conductivity, therefore, in this selection process, without reservoir conditions, engineering conditions (fracturing fluid performance, device pumping capacity ) as well as the evaluation of proppant indoor test results.
A) the selection of proppant Significance and Principles
(1) selection of proppant meaning
Water  Fracturing proppant  of the total operating cost of 1/3 to 1/2, not only oil and gas wells often represent a large portion of the initial cost, and in particular determines the field of oil and gas wells or economic life. Fracturing the overall cost may be too large unnecessary waste of funds, whereas fracturing operations is too small, due to lack of reservoir fluid production, resulting in a well without benefits. After the fracturing fluid is gradually passed, the only thing left in the reservoir is propped fracture proppant to maintain the channel open. Provides a high conductivity of the channel, so that increased oil and gas flow can flow into the wellbore and maintain long-term reservoir flow capacity. Therefore, on the production of fracturing in the water layer optimization design, proppant type and size selection was significant and crucial role
(2) Select the proppant principles should consider the following factors:
① uniform particle size, density.
General, proppants used in hydraulic fracturing is not a single particle size, but there is a certain range of variation, and if sorting proppant poor level, the process of reproduction, plug flow channel, affecting sand filling fracture conductivity, so the proppant particle size and sorting is a certain degree requirements. Commonly used in the domestic mine 20/40 mesh proppant for example, at least 90% of the sand through the sieve after 20 ~ 40 mesh in between, at the same time requires a screen size greater than the first weight is less than 0.1% of the sand, and less than the last The amount of a sieve is not greater than 1%. Ideal density proppant requirements, preferably less than 2000kg/m3, in order to carry sand-carrying fluid to fractures. Strength, crushing rate is small.
Proppant strength is an important indicator of its performance. Since the composition and production of proppant production methods, the intensity differences are large, such as quartz sand strength 21.035.0Mpa, ceramic's strength up 105.0MPa to cracks. After the hydraulic fracturing, fracture closure pressure acting on the proppant fractures, when the proppant strength ratio seam wall formation rock strength is large, there may be embedded proppant stratum; when sewing wall formation rock strength ratio proppant strength, and the closing pressure is greater than the strength of the proppant, the proppant is easily crushed. Both conditions can cause fracture closure or low permeability. So in order to ensure intrinsic fracture conductivity broken filling, closing at different pressures, to a variety of mesh strength proppants have certain requirements and breakage.
③ high roundness and sphericity.
Proppant particle circularity indicates the relative sharpness of the edges, sphericity is similar to the degree of the spherical granules. Roundness and sphericity visual method used to determine, generally 10 to 20 times or under a microscope photomicrograph technique using pictures and then with a standard round, sphericity illustrated contrast, determine round sand, sphericity. With a round ball proppant is not good, its poor penetration of sand filling cracks and corners easily broken, crushed into small particles clog the pores, reducing its permeability.
④ impurity content.
Proppant in the fracture conductivity impurities are harmful. Natural quartz sand impurities, mainly carbonates, feldspar, iron oxides and clay minerals. Generally washed with water, acid (hydrochloric acid soil) to eliminate impurities, treated quartz sand will increase the strength and conductivity.
⑤ proppant selected computer program should be designed Water proppant fracturing is a computer simulation of field experience dealing with the perfect combination. Water fracturing operations costs by proppant fracturing fluids, fracturing process composed of equipment and installation costs. Since proppant costs account for the entire cost of 1/3 to 2/3 is a fact. According closure stress resistance, from a technical point of view, proppant fracturing design choice is not only a key element, but also from the economic point of view but also related to the work of the implementation and effectiveness. While the larger proppant fracturing water conservancy selection and optimization of design, field testing has been used approximation method is repeated in the last ten years, the calculation model of continuous improvement, including significantly improved repayment time and money turnover economic assess the feasibility of the design, including accurate. To obtain a high conductivity and a deep penetration of the cracks, the precise fracturing design is absolutely necessary.
Alone under reservoir conditions for a conventional proppant selection, through the standard characteristic curve analysis and valuation determined proppant.
⑥ proppant nature and in a given geological and engineering conditions, conductivity, fracturing the designer must master the different types and nature of the  Proppant  particle size and its applicable limit. Combined with a given geological conditions (closure pressure, rock hardness, temperature and other physical properties of the target layer fracturing), the choice of the existing engineering conditions (fracturing fluid properties, pumping equipment, etc.) can be safely pumped to a higher pressure after primiparous and stable proppant.
Proppant selected computer program include: general economic criteria; NPV terms; production technology and input data; economic viability of the importance of the model;  Proppant  volume and weight and other factors.
⑦ economic proppant fracturing proppant as one of the materials, in the evaluation of economic benefits will always be a fracturing expenses. Such as the provisions of the fracturing of the repayment schedule (for example, six months or a year) then the designer must compare various fracturing proppant closed under pressure at the same price than [Unit: μm 2 · cm / (Yuan · t) or μm 2 / (RMB · m3)] and the price is higher than the total net income (NPV values) Role and duration. If the particle size of a certain type of proppant pay the specified requirement could be met within the time, then that can be used as the proppant proppant one candidate.