ment will remove gas from the drilling fluid and thereby eliminate the interfer- 

 ence of recycled gas. 



Circulating Pits 



Properly designed and maintained circulating pits (fig. 35-4) can minimize 

 the need of screens, desanders, centifuges, hydraulic cyclones, and degassers for 

 obtaining satisfactory cutting- and mud-analysis logs. Pits can be designed that 

 will permit settling of all solid material larger than 200 mesh from the drilling 

 fluid as well as permit the escape of entrained air and gas. To accomplish the 

 most efficient functioning of these pits, one should take every precaution to 

 prevent channel flow and to provide sheet or bank-to-bank flow, with numerous 

 falls through the pits. Bank-to-bank flow keeps the drilling fluids in the pits 

 in continuous progressive movement and facilitates the droppings of cuttings, 

 sand, and silt, and facilitates the escape to the surface of the drilling fluid 

 the entrained air, gas, and oil. Sheet or bank-to-bank flow with numerous 

 falls is easily accomplished by providing removable tiered partitions at the 

 proper ends of the pits as shown in Figure 35-4. 



Refuse-Reclamation-Reserve Pit 



Occasionally drilling fluids are circulated through a properly designed 

 refuse-reclamation-reserve pit, commonly called a reserve pit, to effect maximum 

 removal of cuttings, sand, silt, entrained gas, air, and oil from a drilling fluid. 



A 



L 



i\ 



TfV^ 



L ( 



□ □ 



^tr. 





== A 



SHALE - SAND FINE SAND-SILT SUCTION 



Figure 35-4. Circulating pits for rotary drilling fluids. 



731 



