DESIGNING A SOLIDS GONTROL SYSTEM ON THE ESD

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The ESD offers unique flexibility when devising a solids control system.

solids control system

When configuring a problem using the simulator the user can choose one of many drilling rigs in the ESD database. An inventory of equipment complete with physical dimensions and performance characteristic are available for each rig that is in the simulator. Upon selection of a rig, the system is initialized with the rig’s tank format and dimension, brand and model of all pumps and solids control devices, and dimensions and configuration of the high and low pressure mud systems. Consideration then is given to the other design inputs of the drilling program potentially affecting solids control, such as:

  1. Pump flow rate.
  2. Anticipated rate of penetration.
  3. Mud weight limitations.
  4. Restrictions on fluid discharge to the reserve pit.

These items control what kind of equipment is required and how it should be best arranged and operated.

drilling pit

The ESD offers unique flexibility when devising a solids control system. The existing equipment can be routed in any fashion taking auction from any compartment and then discharging into any other compartment including the one the suction is taken from. It is possible to route all Liquid underflows either to the reserve pit or to other equipment. Additional equipment can be added to the rig. For example, if a simulation indicates for a given flow rate, penetration rate and mud viscosity that the rig’s shakers can handle the flow with only 40 mesh screens then it is possible to consider multiple shale shakers  arranged in series (cascading) or in parallel. Screen types and sizes can be changed as well as screen angle for shakers with adjustable screen decks.

Up to seven banks of desanders and desilters and five centrifuges can be modelled in a system simultaneously. The centrifugal pump model and pressure loss through the low pressure mud system dictate flow rate and available head at the hydrocyclone inlet manifold. It is possible to design and then analyze almost any combination of centrifugal pumps, motor speeds, motor sizes, impeller sizes and circulation arrangements. Total throughput, available head at the inlet manifold, underflow and overflow rates, percent solids and particle size distributions of all streams can then be analyzed and the best arrangement chosen. This process is easily repeatable, as well operating conditions affecting solids control change, such as weighting the mud with barite.

The design of the ESD is particularly useful for operating and optimizing the performance of centrifuges. Without laboratory equipment at the rig site, it is cumbersome to evaluate centrifuge performance as a function of different operating conditions. A proper field evaluation would require precise mass flow measurements, retort analysis and particle size distributions of all streams. For example, in an un-weighted system, centrifuges may be operated either for the finest possible median cut point or for maximum solids discharge rate or it may be set to produce the driest possible discharge. Dimensions and ranges of the various settings for five popular oilfield centrifuges are currently in the ESD. The user makes selections for speed, fluid pool depth, mud input rate from the tanks, and dilution rate.

The effectiveness of a solids control system is not measured by merits of any single piece of equipment but rather by how the mud at the suction tank compares to mud entering the tanks at the flow line or by other criteria such as the minimum amount of fluid discarded to the reserve pit. Analysis can be accomplished on the ESD at two levels. Real time equipment performance analysis permits immediate cause and effect observations when changing operating parameters of any device. Interval performance, or performance as a function of time and depth, can track long term trends with a given solids control and mud system while drilling a particular hole interval. One of the other important effects that can be observed is the interaction of the other parts of the drilling system with the solids control system. For instance, the increase in rate of penetration with a decrease in mud weight can be quantified.

Solids Control system in ESD

Results of real time analysis are viewed graphically on the ESD’S touchpad graphics plates. Primary applications of real time, or instantaneous analysis, are for sizing equipment for the desired capacity and for performance comparisons of different operating conditions. The ESD enables the user to observe the particle size distribution of the incoming mud system and the predicted output stream (the flow stream that returns to the mud system) at each particular set of operating conditions. The particle size distributions are predicted as well as the mass flow rates of solids and liquids for the output and discard stream. Amounts of solids and liquids discarded are accumulated and costs assigned per unit volume for disposal. Daily rental costs are assigned for solids control equipment added to the rig. The operator can then make a variety of cost/benefit analyzes to optimize operating conditions.

Mud Guns

Mud guns manifold system allows mud to be transported from the suction compartment and/or the mixing compartment to any other compartment and to the mud hopper, a pair of centrifugal pump, working in parallel, move the mud. The flow versus head curve of each pump is approximated with a polynomial and each mud gun nozzle is modeled with the equation; HEAD = λQ1.85. Where λ may vary from nozzle to nozzle. Any other losses in the manifold are assumed negligible. The pump polynomials and the nozzle equations are combined to yield a pair of non-linear algebraic equations. The system of equations is solved iteratively with Newton’s method to determine the operating point of each pump and the flow through each nozzle. Solids settling velocity in a compartment varies inversely with the compartment’s mud gun nozzle velocity.

Mud Guns
Mud Guns

Mud Cleaner

A mud cleaner, a bank of hydrocyclone positioned over a fine-screen shale shaker, is modeled.

The model is simply a “bolting together” of hydrocyclone and shale shaker models. The mud cleaner is usually employed for barite salvage with weighted mud systems, but may be used with any mud system.

mud cleaner

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